Cancellation of interference in a communication system with application to S-CDMA

ABSTRACT

Cancellation of interference in a communication system with application to S-CDMA. A relatively straight-forward implemented, and computationally efficient approach of selecting a predetermined number of unused codes is used to perform weighted linear combination selectively with each of the input spread signals in a multiple access communication system. If desired, the predetermined number of unused codes is always the same in each implementation. Alternatively, the predetermined number of unused codes are selected from within a reordered code matrix using knowledge that is shared between the two ends of a communication system, such as between the CMs and a CMTS. While the context of an S-CDMA communication system having CMs and a CMTS is used, the solution is generally applicable to any communication system that seeks to cancel narrowband interference. Several embodiments are also described that show the generic applicability of the solution across a wide variety of systems.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present U.S. Utility Patent Application claims prioritypursuant to 35 U.S.C. §119(e) to U.S. Provisional Patent ApplicationSerial No. 60/367,564, entitled “CANCELLATION OF INTERFERENCE IN ACOMMUNICATION SYSTEM WITH APPLICATION TO S-CDMA,” (Attorney Docket No.BP 2285), filed Mar. 26, 2002, pending, which is hereby incorporatedherein by reference in its entirety and is made part of the present U.S.Utility Patent Application for all purposes.

TECHNICAL FIELD OF THE INVENTION

[0002] The invention relates generally to communication systems; and,more particularly, it relates to communication systems that may beaffected by undesirable interference.

BACKGROUND OF THE INVENTION

[0003] Signal processing within communication systems having acommunication channel, in an effort to improve the quality of signalspassing through the communication channel, has been under developmentfor many years. In the past several years, emphasis has moved largely tothe domain of digital communication systems that modulate bit streamsinto an analog signal for transmission over a communication channel.This channel can be a variety of channel types. Many differentapproaches are employed in the prior art to try to minimize orsubstantially reduce the effects of interference that may be introducedinto a signal that is transmitted within across a communication channel.In particular, the prior art approaches that seek to performcancellation of interference that occupies a small number of signaldimensions in a signal are typically deficient for a number of reasonsas is briefly referenced below. One particular type of interference thatthese prior art schemes seek to minimize is the narrowband interferencethat is sometimes referred to as ingress interference. Another type ofnarrowband interference that may be problematic is the interference ofimpulse/burst noise. Yet another type of interference that may beproblematic is within the code division multiple access (CDMA) contextwhen the interference is on a small number of codes.

[0004] One of the main methods employed in the prior art to eliminatethis interference is the use of a notch filter. This solution issufficient in some applications, but the notch filter itself oftentimescauses distortion of the desired signal. In the CDMA context, thisdistortion is called inter-code interference (ICI). Then, another meansmust oftentimes be included to remove the very ICI that has beenintroduced by the notch filter. One way to do this is to de-spread thesignal. Then, hard decisions are made using the de-spread signal. Thehard decisions are then respread and passed through the notch filter andto subtract from the original signal to remove the estimated distortion.In some instances, this process is repeated numerous times to try toachieve an adequate result.

[0005] These prior art approaches described above are deficient in thatthey suffer the effect of the nonlinearity (hard decision device) whichis applied to the signal. The nonlinearity is prone to make incorrectdecisions, requiring many iterations before the process converges, if itever converges at all.

[0006] Further limitations and disadvantages of conventional andtraditional systems will become apparent through comparison of suchsystems with the invention as set forth in the remainder of the presentapplication with reference to the drawings.

SUMMARY OF THE INVENTION

[0007] Various aspects of the invention can be found in a communicationreceiver that supports interference cancellation functionality. Thepresent invention uses a linear combination of the unused dimensions(for example, the unused codes) to cancel the interference. This may bedone after the de-spreader, or, equivalently, as part of thede-spreading process. There is no appreciable inter-code interferenceintroduced and no decision errors are made as part of this process. Theallocation of unused codes reduces the capacity of the system by a smallamount. In one embodiment, the reduction of capacity of the system willbe to 120/128 of the original capacity for a system of 128 codes where 8unused codes are employed. Clearly, other numbers of available codes mayalso be employed without departing from the scope and spirit of theinvention.

[0008] It is noted that the present invention may be extended across awide variety of application contexts. The present technique can beapplied to cancel not only narrowband interference, but any interferencethat occupies a small number of dimensions in the signal space. Thenarrowband interference includes just one of the many types ofinterferences that may be substantially cancelled according to thepresent invention. A narrowband signal occupies a small number of DFT(discrete Fourier transform) bins, showing that it occupies a smallnumber of dimensions in signal space. An extremely simple example is aCW (Continuous Wave) signal whose frequency is an integer multiple ofthe de-spread symbol rate; this CW signal occupies only a single bin inthe DFT, or only one dimension in the signal space, where each dimensionis, in this case, one DFT bin. Another example is a short burst of noise(impulse or burst noise). A short burst signal occupies a small numberof time samples, again showing that it too occupies a small number ofdimensions, where each dimension is, in this case, a time sample.

[0009] Other types of signals may be constructed, without limit, thatsatisfy the property that they occupy a small number of dimensions intheir respective signal space. All such signals can be canceled by thepresent technique. It is noted that the DFT is just one example of anorthonormal expansion. A second example is the code matrix in DOCSIS 2.0S-CDMA. A third example may be the identity matrix. Innumerable otherorthonormal transforms also exist that are used to transform a signalinto a finite signal space. If a signal occupies a small number ofdimensions in any orthonormal transformation, the interferencecancellation performed according to the present invention may be usedfor canceling it. It is noted here that orthogonal transformations mayalso be used without departing from the scope and spirit of theinvention in any way within embodiments where normalization of not ofconcern or of low priority.

[0010] A number of specific embodiments are illustrated to show theversatility and wide applicability of the present invention across avariety of communication systems contexts. However, it is generallynoted that the present invention may be practiced within anycommunication system that seeks to perform interference cancellationwhen the communication system employs signaling that occupies a smallnumber of dimensions in the communication signal's space.

[0011] In addition, other aspects, advantages and novel features of theinvention will become apparent from the following detailed descriptionof the invention when considered in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] A better understanding of the invention can be obtained when thefollowing detailed description of various exemplary embodiments isconsidered in conjunction with the following drawings.

[0013]FIG. 1 is a system diagram illustrating an embodiment of a cablemodem (CM) communication system that is built according to the presentinvention.

[0014]FIG. 2 is a system diagram illustrating another embodiment of a CMcommunication system that is built according to the present invention.

[0015]FIG. 3A is a system diagram illustrating an embodiment of acellular communication system that is built according to the presentinvention.

[0016]FIG. 3B is a system diagram illustrating another embodiment of acellular communication system that is built according to the presentinvention.

[0017]FIG. 4 is a system diagram illustrating an embodiment of asatellite communication system that is built according to the presentinvention.

[0018]FIG. 5A is a system diagram illustrating an embodiment of amicrowave communication system that is built according to the presentinvention.

[0019]FIG. 5B is a system diagram illustrating an embodiment of apoint-to-point radio communication system that is built according to thepresent invention.

[0020]FIG. 6 is a system diagram illustrating an embodiment of a highdefinition (HDTV) communication system that is built according to thepresent invention.

[0021]FIG. 7 is a system diagram illustrating an embodiment of acommunication system that is built according to the present invention.

[0022]FIG. 8 is a system diagram illustrating another embodiment of acommunication system that is built according to the present invention.

[0023]FIG. 9 is a system diagram illustrating an embodiment of a cablemodem termination system (CMTS) system that is built according to thepresent invention.

[0024]FIG. 10 is a system diagram illustrating an embodiment of a burstreceiver system that is built according to the present invention.

[0025]FIG. 11 is a system diagram illustrating an embodiment of a singlechip DOCSIS/EuroDOCSIS CM system that is built according to the presentinvention.

[0026]FIG. 12 is a system diagram illustrating another embodiment of asingle chip DOCSIS/EuroDOCSIS CM system that is built according to thepresent invention.

[0027]FIG. 13 is a system diagram illustrating an embodiment of a singlechip wireless modem system that is built according to the presentinvention.

[0028]FIG. 14 is a system diagram illustrating another embodiment of asingle chip wireless modem system that is built according to the presentinvention.

[0029]FIG. 15 is a diagram illustrating an embodiment of a vectorde-spreader that is built according to the present invention.

[0030]FIG. 16 is a diagram illustrating an embodiment of an interferencecanceler that is built according to the present invention.

[0031]FIG. 17 is a diagram illustrating another embodiment of aninterference canceler that is built according to the present invention.

[0032]FIG. 18 is a diagram illustrating another embodiment of aninterference canceler that is built according to the present invention.

[0033]FIG. 19 is a diagram illustrating an embodiment of an interferencecanceler with memory that is built according to the present invention.

[0034]FIG. 20 is a diagram illustrating an embodiment of equalizationwith canceler that is arranged according to the present invention.

[0035]FIG. 21 is a diagram illustrating an embodiment of Least MeansSquare (LMS) training of an interference canceler according to thepresent invention.

[0036]FIG. 22A is a diagram illustrating an embodiment of signaltransformation according to the present invention.

[0037]FIG. 22B is a diagram illustrating another embodiment of signaltransformation according to the present invention.

[0038]FIG. 23 is an operational flow diagram illustrating an embodimentof an interference cancellation method that is performed according tothe present invention.

[0039]FIG. 24 is an operational flow diagram illustrating anotherembodiment of an interference cancellation method that is performedaccording to the present invention.

[0040]FIG. 25 is an operational flow diagram illustrating an embodimentof an unused code selection method that is performed according to thepresent invention.

[0041]FIG. 26 is an operational flow diagram illustrating an embodimentof an S-CDMA interference cancellation method that is performedaccording to the present invention.

[0042]FIG. 27 is an operational flow diagram illustrating anotherembodiment of an interference cancellation method that is performedaccording to the present invention.

[0043]FIG. 28 is a diagram illustrating an embodiment of a spectrum ofnarrowband interference that may be addressed and overcome whenpracticing via the present invention.

[0044]FIG. 29 is a diagram illustrating an embodiment of a spectrum ofadapted code showing null at a location of interference that may beachieved when practicing via the present invention.

[0045]FIG. 30A is a diagram illustrating an embodiment of a receivedconstellation before interference has been cancelled when practicing viathe present invention.

[0046]FIG. 30B is a diagram illustrating an embodiment of a receivedconstellation after interference has been cancelled when practicing viathe present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0047] The present invention provides a solution for interferencecancellation for communication systems (where a medium is used by oneuser or if shared among many users). More specifically, the presentinvention is applicable within code-division multiple access (CDMA)communication systems, as well as synchronous code-division multipleaccess (S-CDMA) communication systems. One particular type of S-CDMAcommunication system that may benefit from the present invention is theData Over Cable Service Interface Specifications (DOCSIS) version 2.0S-CDMA that is operable for communication systems. The present inventionpresents a solution that provides for cancellation of interference inany such communication systems. The interference cancellation may beviewed as being directed primarily towards the type of interference thatoccupies a small number of signal dimensions. Examples of such types ofinterference include narrowband interference (herein also referred to asingress) or impulse/burst noise. The present invention also provides asolution where it may operate in the presence of simultaneous narrowbandinterference and impulse/burst noise and to substantially eliminate themboth.

[0048] The present invention provides an approach for interferencecancellation that provides a number of benefits including a completelylinear method of canceling ingress that employed no DFE (DecisionFeedback Equalizer) or SIC (Successive Ingress Cancellation). Thisapproach can cancel wideband ingress and may be implemented in arelatively simple and efficient structure. Moreover, the presentinvention may be combined relatively easily, given its simple andefficient structure, with other methods and systems that may assist inthe interference cancellation.

[0049] The present invention uses a linear combination of the unuseddimensions (for example, the unused codes) to cancel the interference.This may be done after the de-spreader, or, equivalently, as part of thede-spreading process. There is no appreciable inter-code interferenceintroduced and no decision errors are made as part of this process. Theallocation of unused codes reduces the capacity of the system by a smallamount; for example, to 120/128 of the original capacity for a system of128 codes where 8 unused codes are employed.

[0050] It is noted here that the specific examples of 120 active codes,and 8 unused codes in a system having 128 available codes is exemplary.Clearly, other embodiments may be employed (having different numbers ofcodes—both different numbers of used and unused) without departing fromthe scope and spirit of the invention.

[0051] From certain perspectives, the present invention may be viewed asbeing an extension of sub-dimensional modulation that is employed forTDMA (Time Division Multiple Access), and it may then be extended toS-CDMA (Synchronous Code Division Multiple Access). To begin thisdiscussion, we consider an example case where 120 active codes are usedand narrowband ingress (narrowband interference) is present. Theremaining 8 codes are then transmitted as true zero symbols. At thereceiver, the unused 8 codes are received with samples of the narrowbandingress. This information may then be used to cancel the ingress in thesame manner that is used in sub-dimensional modulation. The 8 unusedcodes are considered as extra dimensions and the receiver is trainedbased on this information.

[0052] We continue on with 128 code example (8 of the codes beingunused). By employing the 8 unused spreading codes, linear combinationsof these 8 codes may be added to any other code that is transmitted froma transmitter to a receiver, and the resulting composite waveform can beused for de-spreading that one transmitted code. Since, ideally, nosignal is present on any of these 8 codes (being zero codes), thenlittle or no inter-code interference from the transmitters will beinduced. In AWGN (Additive White Gaussian Noise), the inclusion of theseadditional de-spreading codes serves to merely increase the noise at thedecision slicer for the code of interest. However, in the presence ofinterference, such as narrowband interference, some combination of thesecodes in the de-spreading process is operable to reduce the ingressenough to overcome the increased AWGN and make it worthwhile.Heuristically, the unused codes may correlate somewhat with theinterference, and if so, may be used to “subtract” some component of theinterference at the decision slicer, as a type of noise canceler.

[0053] The similarity of this approach is somewhat analogous to thefunctionality of an ICF (Ingress Cancellation Filter). In certainembodiments, a TDMA-only, CDMA-only, and/or a TDMA/CDMA burst receivermay be leveraged for this S-CDMA application, including the use of theTrench method or derivative that is mentioned below.

[0054] It is noted that the approach to reducing the interference powerat the decision point using only the unused codes may not be optimal incertain embodiments, since using codes with data carried on them mayoffer some interference rejection overcoming the introduction of thetransmitter inter-code interference. It is also noted that including “inuse” codes would actually provide benefit in practical situations.

[0055] It is also noted that using a strict LMS (Least Means Square)type of approach to converging 128 taps to the desired de-spreading codemay prove laborious (in terms of requiring many iterations). Thisapproach does not focus on just the unused codes, and has far manydegrees of freedom than just finding 8 coefficients for the weightingsof the 8 unused codes.

[0056] Analysis has shown that indeed there is great similarity in theformulation and solution of the optimal taps in the monic filter of theICF for ingress cancellation, and in this application of unusedspreading codes in ingress cancellation for S-CDMA. Both can beformulated in a LS (Least Squares) type of problem, with the ensuingtypical solution taking form.

[0057] One advantage that may arise for the TDMA ICF case is when thematrix to be inverted is Toeplitz (a Toeplitz matrix in addition amatrix in which all the elements are the same along any diagonal thatslopes from northwest to southeast), and thus admits significantcomputational advantages, such as discovered by William Trench.

[0058] However, in the S-CDMA formulation with unused codes, the matrixto be inverted is not Toeplitz, and the Trench approach does not apply.There still may be some computational advantages due to the underlyingconstruction of the matrix to be inverted, but it may be that only thetraditional numerical methods such as Cholesky decomposition mayintroduce simplification. The matrix to be inverted is at least of theform C^(T)RC, where C=128×8, with each column orthogonal with the others(a sub-matrix of a Unitary matrix), and R=128×128 and IS Toeplitz, andT=complex conjugate.

[0059] One implementation of the present invention may be described asshown below.

[0060] Let R=R_(m,n)=E{r*(m) r(n)}, where r(n) are noise and ingresssamples, containing little or no signal. R is 128×128, where the samplescorrespond to the noise in the chips of a spreading interval. Thesymbol * denotes complex conjugate. This is the noise (or noise plusinterference) covariance matrix.

[0061] Let C=[c1 c2 c3 c4 c5 c6 c7 c8], where ci=column of 128 chips ofi^(th) unused spreading code. C is 128 rows by 8 columns.

[0062] Let:

[0063] dsc_(opt)=optimal de-spreading code for code-of-interest c_(k),(written alternatively below)

[0064] dsc_(opt)=C_(k)+w₁cl+w₂c2+ . . . +w₈c8,

[0065] where dsc_(opt) is a column vector with 128 components, and w,are scalar weighting coefficients.

[0066] Thus, dsc_(opt)=[1 w₁ w₂ . . . w₈][C_(k) c1 c2 . . . c8], and wecan see that the optimal solution for the S-CDMA case indeed has a formsimilar to the monic filter in the TDMA ICF solution.

[0067] Let w_(opt)=[w₁ w₂ . . . w₈] which provides the optimalde-spreading for signaling with the k^(th) spreading code.

[0068] It can be shown that w_(opt)=−[C^(T)RC]⁻¹[C^(T)R]c_(k), where allthe vectors, matrices, and notation are as defined above.

[0069] It is noted that with the ICF in TDMA,

[0070] w_(opt)=−[R]⁻¹[r1 r2 r3 . . . r16]T, where $R = \begin{bmatrix}{r0} & {r1} & {r2} & \ldots & {r16} \\{{r1}*} & {r0} & {r1} & \ldots & {r15} \\\vdots & \quad & \quad & ⋰ & \vdots \\{{r16}*} & {{r15}*} & \ldots & {{r1}*} & {r0}\end{bmatrix}$

[0071] Another characteristic of the present invention is that thecomplexity of the method with the LS approach is severe for largematrices compared to the ICF and Trench method with TDMA. However, thiscomplexity is mitigated by the reduced matrix size resulting from thesub-space projection approach described here and below. From certainperspectives, the S-CDMA approach with unused codes may be viewed as notlending itself to the computational efficiencies of Trench approach orits derivatives.

[0072] However, using an LMS tap update approach has been found to work.The weights of the unused spreading codes, wi, are updated in LMSfashion. In this method, the de-spreader for the code of interest isinput to a decision slicer. The resulting complex error is computed.Similarly, each unused spreading code has its corresponding de-spreadingoperating. The result of the de-spreader corresponding to an unusedspreading code is “signal,” just as the “signal” rests in the variousshift registers in the conventional FIR (Finite Impulse Response) filterin the normal LMS. The de-spread outputs for each of the unused codes ismultiplied by the error vector, and then multiplied by a step sizefactor “-mu” and added to the existing tap weight, to update the tapweight.

[0073] With 8 unused spreading codes, there is a set of 8 tap weightsfor each used spreading code. Thus, with the 8 unused spreading codes,there are 8×120 tap weights to iterate.

[0074] This approach is much less computationally intensive than usingan LS-based. The S-CDMA LMS approach introduces little additionalcomputation when compared to operating the de-spreading codesthemselves. This approach is beneficial for a number of reasons. It iscomputationally acceptable, in that, it limits the number of taps toonly 8 (in our continuing example of 8 unused spreading codes), whichalmost certainly provides much more rapid convergence and less “tapnoise.” In addition, it eliminates from the search for optimalcoefficients in the de-spreader those codes that are known to correspondto used codes.

[0075]FIG. 1 is a system diagram illustrating an embodiment of a CMcommunication system 100 that is built according to the presentinvention. The CM communication system includes a number of CMs (shownas a CM user #1 111, a CM user #2 115, . . . , and a CM user #n 121) anda CMTS 130. The CMTS 130 is a component that exchanges digital signalswith CMs on a cable network.

[0076] Each of a number of CM users, shown as the CM user #1 111, the CMuser #2 115, and the CM user #n 121, is able to communicatively coupleto a CM network segment 199. A number of elements may be included withinthe CM network segment 199. For example, routers, splitters, couplers,relays, and amplifiers may be contained within the CM network segment199 without departing from the scope and spirit of the invention.

[0077] The CM network segment 199 allows communicative coupling betweena CM user and a cable headend transmitter 120 and/or a CMTS 130. In someembodiments, a cable CMTS is in fact contained within a headendtransmitter. In other embodiments, the functionality of the cable CMTSand the headend transmitter are represented as two distinct functionalblocks so that their respective contribution may be more easilyappreciated and understood. This viewpoint is shown in the situationwhere the CMTS 130 is pictorially shown as being located externally to acable headend transmitter 120. In the more common representation andimplementation, a CMTS 135 is located within the cable headendtransmitter 120. The combination of a CMTS and a cable headendtransmitter may be referred to as being the “cable headend transmitter;”it then being understood that the cable headend transmitter supports theCMTS functionality. The CMTS 130 may be located at a local office of acable television company or at another location within a CMcommunication system. In the following description, the CMTS 130 is usedfor illustration; yet, the same functionality and capability asdescribed for the CMTS 130 may equally apply to embodiments thatalternatively employ the CMTS 135. The cable headend transmitter 120 isable to provide a number of services including those of audio, video,telephony, local access channels, as well as any other service known inthe art of cable systems. Each of these services may be provided to theone or more CM users 111, 115, . . . , and 121.

[0078] In addition, through the CMTS 130, the CM users 111, 115, . . . ,121 are able to transmit and receive data from the Internet, . . . ,and/or any other network to which the CMTS 130 is communicativelycoupled. The operation of a CMTS, at the cable-provider's head-end, maybe viewed as providing many of the same functions provided by a digitalsubscriber line access multiplexor (DSLAM) within a digital subscriberline (DSL) system. The CMTS 130 takes the traffic coming in from a groupof customers on a single channel and routes it to an Internet ServiceProvider (ISP) for connection to the Internet, as shown via the Internetaccess. At the head-end, the cable providers will have, or lease spacefor a third-party ISP to have, servers for accounting and logging,dynamic host configuration protocol (DHCP) for assigning andadministering the Internet protocol (IP) addresses of all the cablesystem's users, and typically control servers for a protocol called DataOver Cable Service Interface Specifications (DOCSIS), the major standardused by U.S. cable systems in providing Internet access to users.

[0079] The downstream information flows to all of the connected CM users111, 115, . . . , 121; this may be viewed to be in a manner that issimilar to that manner within an Ethernet network. The individualnetwork connection, within the CM network segment 199, decides whether aparticular block of data is intended for it or not. On the upstreamside, information is sent from the CM users 111, 115, . . . , 121 to theCMTS 130; on this upstream transmission, the users within the CM users111, 115, . . . , 121 to whom the data is not intended do not see thatdata at all. As an example of the capabilities provided by a CMTS, theCMTS will enable as many as 1,000 users to connect to the Internetthrough a single 6 MHz channel. Since a single channel is capable of30-40 megabits per second of total throughput, this means that users maysee far better performance than is available with standard dial-upmodems. Embodiments implementing the present invention are describedbelow and in the various Figures that show the data handling and controlwithin one or both of a CM and a CMTS within a CM system that operatesby employing S-CDMA (Synchronous Code Division Multiple Access).

[0080] The CMs of the CM users 111, 115, . . . , 121 and the CMTS 130communicate synchronization information to one another to ensure properalignment of transmission from the CM users 111, 115, . . . , 121 to theCMTS 130. This is where the synchronization of the S-CDMA communicationsystems is extremely important. When a number of the CMs all transmittheir signals at a same time such that these signals are received at theCMTS 130 on the same frequency and at the same time, they must all beable to be properly de-spread and decoded for proper signal processing.

[0081] Each of the CMs users 111, 115, . . . , 121 is located arespective transmit distance from the CMTS 130. In order to achieveoptimum spreading diversity and orthogonality for the CMs users 111,115, . . . , 121 to transmission of the CMTS 130, each of the CMtransmissions must be synchronized so that it arrives, from theperspective of the CMTS 130, synchronous with other CM transmissions. Inorder to achieve this goal, for a particular transmission cycle, each ofthe CMs 111, 115, . . . , 121 will typically transmit to the CMTS 130 ata respective transmission time, which will likely differ from thetransmission times of other CMs. These differing transmission times willbe based upon the relative transmission distance between the CM and theCMTS 130. These operations may be supported by the determination of theround trip delays (RTPs) between the CMTS 130 and each supported CM.With these RTPs determined, the CMs may then determine at what point totransmit their S-CDMA data so that all CM transmissions will arrivesynchronously at the CMTS 130.

[0082] The present invention enables interference cancellation withinthe CMTS 130, as shown in a functional block 131. The present inventionmay also be implemented to support interference cancellation within anyone of the CMs 111, 115, . . . , 121; the particular implementation ofinterference cancellation is shown as a functional block 122 within theCM 122, yet it is understood that the interference cancellationfunctionality may also be supported within the other CMs as well. TheCMTS 130 receives an input spread signal and is operable to performdispreading and interference cancellation according to the presentinvention. The CMTS 130 is operable to employ a linear combiner, thatuses as inputs complex valued combining weights to the particular codesthat are selectively used to assist in the interference cancellation ofone of the de-spread signals that is de-spread from the input spreadsignal that the CMTS 130 receives. Alternatively, the present inventionmay be viewed as employing at least one of an adapted code and anadapted code matrix to perform interference cancellation according tothe present invention.

[0083]FIG. 2 is a system diagram illustrating another embodiment of a CMcommunication system 200 that is built according to the presentinvention. From certain perspectives, the FIG. 2 may be viewed as acommunication system allowing bi-directional communication between acustomer premise equipment (CPE) 240 and a network. In some embodiments,the CPE 240 is a personal computer or some other device allowing a userto access an external network. The network may be a wide area network(WAN) 280, or alternatively, the Internet 290 itself. For example, theCM communication system 200 is operable to allow Internet protocol (IP)traffic to achieve transparent bi-directional transfer between aCMTS-network side interface (CMTS-NSI: viewed as being between the CMTS230 and the Internet 290) and a CM to CPE interface (CMCI: viewed asbeing between the CM 210 and the CPE 240).

[0084] The WAN 280, and/or the Internet 290, is/are communicativelycoupled to the CMTS 230 via a CMTS-NSI. The CMTS 230 is operable tosupport the external network termination, for one or both of the WAN 280and the Internet 290. The CMTS 230 includes a modulator and ademodulator to support transmitter and receiver functionality to andfrom a CM network segment 299. The receiver functionality within theCMTS 230 is operable to support interference cancellation functionality231 according to the present invention. It is also noted that there maybe embodiment where the CM 210 is also operable to support interferencecancellation functionality using the present invention, as shown by afunctional block 211. Implementing interference cancellation in thetransmitter prevents noise enhancement that occurs when interferencecancellation is performed in the receiver.

[0085] A number of elements may be included within the CM networksegment 299. For example, routers, splitters, couplers, relays, andamplifiers may be contained within the CM network segment 299 withoutdeparting from the scope and spirit of the invention. The CM networksegment 299 allows communicative coupling between a CM user and the CMTS230. The FIG. 2 shows just one of many embodiments where theinterference cancellation, performed according to the present invention,may be performed to provide for improved operation within acommunication system.

[0086]FIG. 3A is a system diagram illustrating an embodiment of acellular communication system 300A that is built according to thepresent invention. A mobile transmitter 310 has a local antenna 311. Themobile transmitter 310 may be any number of types of transmittersincluding a cellular telephone, a wireless pager unit, a mobile computerhaving transmit functionality, or any other type of mobile transmitter.The mobile transmitter 310 transmits a signal, using its local antenna311, to a base station receiver 340 via a wireless communicationchannel. The base station receiver 340 is communicatively coupled to areceiving wireless tower 349 to be able to receive transmission from thelocal antenna 311 of the mobile transmitter 310 that have beencommunicated via the wireless communication channel. The receivingwireless tower 349 communicatively couples the received signal to thebase station receiver 340.

[0087] The base station receiver 340 is then able to supportinterference cancellation functionality according to the presentinvention, as shown in a functional block 341, on the received signal.The FIG. 3A shows yet another of the many embodiments where theinterference cancellation, performed according to the present invention,may be performed to provide for improved operation within acommunication system.

[0088]FIG. 3B is a system diagram illustrating another embodiment of acellular communication system that is built according to the presentinvention. From certain perspectives, the FIG. 3B may be viewed as beingthe reverse transmission operation of the cellular communication system300B of the FIG. 3A. A base station transmitter 320 is communicativelycoupled to a transmitting wireless tower 321. The base stationtransmitter 320, using its transmitting wireless tower 321, transmits asignal to a local antenna 339 via a wireless communication channel. Thelocal antenna 339 is communicatively coupled to a mobile receiver 330 sothat the mobile receiver 330 is able to receive transmission from thetransmitting wireless tower 321 of the base station transmitter 320 thathave been communicated via the wireless communication channel. The localantenna 339 communicatively couples the received signal to the mobilereceiver 330. It is noted that the mobile receiver 330 may be any numberof types of transmitters including a cellular telephone, a wirelesspager unit, a mobile computer having transmit functionality; or anyother type of mobile transmitter.

[0089] The mobile receiver 330 is then able to support interferencecancellation functionality according to the present invention, as shownin a functional block 331, on the received signal. The FIG. 3B shows yetanother of the many embodiments where the interference cancellationfunctionality, performed according to the present invention, may beperformed to provide for improved operation within a communicationsystem.

[0090] It is also noted that the embodiments described above within theFIGS. 3A and 3B may operate in conjunction within a single communicationsystem. That is to say, a mobile unit (that supports both transmit andreceive functionality) may be implemented to support interferencecancellation functionality during receipt of signals while the basestation device (that supports both transmit and receive functionality)may also be implemented to support interference cancellationfunctionality during receipt of signals. This way, both devices areoperable to support the interference cancellation functionalityaccording to the present invention at both ends of the communicationlink. This dual-end interference cancellation functionality is also truewithin other of the various embodiments described herein that illustrateboth ends of a communication link.

[0091] It is further noted that the embodiments described above withinthe FIGS. 3A and 3B1 may operate in conjunction within a singlecommunication system from yet another perspective. A mobile transmittermay be implemented to support interference cancellation functionalityduring signal processing and transmission of its signals to a basestation receiver. Similarly, a base station transmitter may beimplemented to support interference cancellation functionality duringsignal processing and transmission of its signals to a mobile unitreceiver. This may be performed, at least in part, by adjusting atransmitted spectrum to meet a desired spectral mask. It may bedesirable to attenuate certain portions of the spectrum using thesubspace canceler. In these applications the canceler is predominantlylocated in the transmitter. Further detail of this interferencecancellation within a transmitter device is presented below. Thisadjusting of a transmitted spectrum to meet a desired spectral mask maybe performed within any of the various embodiments that include atransmitter that transmits a signal to a receiver according to thepresent invention.

[0092]FIG. 4 is a system diagram illustrating an embodiment of asatellite communication system 400 that is built according to thepresent invention. A transmitter 420 is communicatively coupled to awired network 410. The wired network 410 may include any number ofnetworks including the Internet, proprietary networks, and other wirednetworks. The transmitter 420 includes a satellite earth station 451that is able to communicate to a satellite 453 via a wirelesscommunication channel. The satellite 453 is able to communicate with areceiver 430. The receiver 430 is also located on the earth. Here, thecommunication to and from the satellite 453 may cooperatively be viewedas being a wireless communication channel, or each of the communicationto and from the satellite 453 may be viewed as being two distinctwireless communication channels.

[0093] For example, the wireless communication “channel” may be viewedas not including multiple wireless hops in one embodiment. In otherembodiments, the satellite 453 receives a signal received from thesatellite earth station 451, amplifies it, and relays it to the receiver430; the receiver 430 may include terrestrial receivers such assatellite receivers, satellite based telephones, and satellite basedInternet receivers, among other receiver types. In the case where thesatellite 453 receives a signal received from the satellite earthstation 451, amplifies it, and relays it, the satellite 453 may beviewed as being a “transponder.” In addition, other satellites may existthat perform both receiver and transmitter operations. In this case,each leg of an up-down transmission via the wireless communicationchannel would be considered separately. The wireless communicationchannel between the satellite 453 and a fixed earth station would likelybe less time-varying than the wireless communication channel between thesatellite 453 and a mobile station.

[0094] In whichever embodiment, the satellite 453 communicates with thereceiver 430. The receiver 430 may be viewed as being a mobile unit incertain embodiments (employing a local antenna 412); alternatively, thereceiver 430 may be viewed as being a satellite earth station 452 thatmay be communicatively coupled to a wired network in a similar mannerthat the satellite earth station 451, within the transmitter 420,communicatively couples to a wired network. In both situations, thereceiver 430 is able to support interference cancellation functionality,as shown in a functional block 431, according to the present invention.For example, the receiver 430 is able to perform interferencecancellation, as shown in a functional block 431, on the signal receivedfrom the satellite 453. The FIG. 4 shows yet another of the manyembodiments where the interference cancellation, performed according tothe present invention, may be performed to provide for improved receiverperformance.

[0095]FIG. 5A is a system diagram illustrating an embodiment of amicrowave communication system 500A that is built according to thepresent invention. A tower transmitter 511 includes a wireless tower515. The tower transmitter 511, using its wireless tower 515, transmitsa signal to a tower receiver 512 via a wireless communication channel.The tower receiver 512 includes a wireless tower 516. The wireless tower516 is able to receive transmissions from the wireless tower 515 thathave been communicated via the wireless communication channel. The towerreceiver 512 is then able to support interference cancellationfunctionality, as shown in a functional block 533. The FIG. 5A shows yetanother of the many embodiments where interference cancellation,performed according to the present invention, may be performed toprovide for improved receiver performance.

[0096]FIG. 5B is a system diagram illustrating an embodiment of apoint-to-point radio communication system 500B that is built accordingto the present invention. A mobile unit 551 includes a local antenna555. The mobile unit 551, using its local antenna 555, transmits asignal to a local antenna 556 via a wireless communication channel. Thelocal antenna 556 is included within a mobile unit 552. The mobile unit552 is able to receive transmissions from the mobile unit 551 that havebeen communicated via the wireless communication channel. The mobileunit 552 is then able to support interference cancellationfunctionality, as shown in a functional block 553, on the receivedsignal. The FIG. 5B shows just yet another of the many embodiments whereinterference cancellation, performed according to the present invention,may be performed to provide for improved receiver performance.

[0097]FIG. 6 is a system diagram illustrating an embodiment of a highdefinition (HDTV) communication system 600 that is built according tothe present invention. An HDTV transmitter 610 includes a wireless tower611. The HDTV transmitter 610, using its wireless tower 611, transmits asignal to an HDTV set top box receiver 620 via a wireless communicationchannel. The HDTV set top box receiver 620 includes the functionality toreceive the wireless transmitted signal. The HDTV set top box receiver620 is also communicatively coupled to an HDTV display 630 that is ableto display the demodulated and decoded wireless transmitted signalsreceived by the HDTV set top box receiver 620.

[0098] The HDTV set top box receiver 620 is then able to supportinterference cancellation functionality, as shown in a functional block623 to provide for improved receiver performance. The FIG. 6 shows yetanother of the many embodiments where interference cancellation,performed according to the present invention, may be performed toprovide for improved receiver performance.

[0099]FIG. 7 is a system diagram illustrating an embodiment of acommunication system that is built according to the present invention.The FIG. 7 shows communicative coupling, via a communication channel799, between two transceivers, namely, a transceiver 701 and atransceiver 702. The communication channel 799 may be a wirelinecommunication channel or a wireless communication channel.

[0100] Each of the transceivers 701 and 702 includes a transmitter and areceiver. For example, the transceiver 701 includes a transmitter 749and a receiver 740; the transceiver 702 includes a transmitter 759 and areceiver 730. The receivers 740 and 730, within the transceivers 701 and702, respectively, are each operable to support interferencecancellation functionality according to the present invention. This willallow improved signal processing for both of the transceivers 701 and702. For example, the receiver 740, within the transceiver 701, is ableto support interference cancellation functionality, as shown in afunctional block 741, on a signal received from the transmitter 759 ofthe transceiver 702. Similarly, the receiver 730, within the transceiver702, is able to support interference cancellation functionality, asshown in a functional block 731, on a signal received from thetransmitter 749 of the transceiver 701.

[0101] If desired in certain embodiments, the transmitters 749 and 759,within the transceivers 701 and 702, respectively, are each operable tosupport interference cancellation functionality according to the presentinvention. This will also allow improved signal processing for both ofthe transceivers 701 and 702. For example, the transmitter 749, withinthe transceiver 701, is able to support interference cancellationfunctionality, as shown in a functional block 748, on a signal that isto be transmitted from the transmitter 759 of the transceiver 702.Similarly, the transmitter 759, within the transceiver 702, is able tosupport interference cancellation functionality, as shown in afunctional block 758, on a signal that is to be transmitted from thetransmitter 759 of the transceiver 702.

[0102] This interference cancellation functionality, within thetransmitters 749 and 759, respectively, may be performed, at least inpart, by adjusting a transmitted spectrum to meet a desired spectralmask according to the present invention. The FIG. 7 shows yet another ofthe many embodiments where interference cancellation, performedaccording to the present invention, may be performed to provide forimproved performance.

[0103]FIG. 8 is a system diagram illustrating another embodiment of acommunication system 800 that is built according to the presentinvention. The FIG. 8 shows communicative coupling, via a communicationchannel 899, between a transmitter 849 and a receiver 830. Thecommunication channel 899 may be a wireline communication channel or awireless communication channel. The receiver 830 is operable to supportinterference cancellation, as shown in a functional block 831, accordingto the present invention. The FIG. 8 shows yet another of the manyembodiments where interference cancellation, performed according to thepresent invention, may be performed to provide for improved performance.

[0104] In certain embodiments, the transmitter 849 is also operable tosupport interference cancellation, as shown in a functional block 848,according to the present invention. This interference cancellationfunctionality, within the transmitter 849, may be performed, at least inpart, by adjusting a transmitted spectrum to meet a desired spectralmask according to the present invention. For example, the interferencecancellation functionality of the present invention may be located atthe transmitter 849, the receiver 830, or partly in each (as shown bythe functional blocks 848 and 831). In many of the various embodimentsdescribed herein, the interference cancellation functionality has beenlocated in a receiver of a communication system. The following describesone embodiment of how the interference cancellation functionality may belocated at the transmitter. The unused codes, instead of being modulatedat the transmitter with zero symbols, are modulated with a linearcombination of the desired signals from the used codes. In the case ofnarrowband interference, the resulting transmitted signal will have anull on the interferer.

[0105]FIG. 9 is a system diagram illustrating an embodiment of a CMTSsystem 900 that is built according to the present invention. The CMTSsystem 900 includes a CMTS medium access controller (MAC) 930 thatoperates with a number of other devices to perform communication fromone or more CMs to a WAN 980. The CMTS MAC 930 may be viewed asproviding the hardware support for MAC-layer per-packet functionsincluding fragmentation, concatenation, and payload header suppressionthat all are able to offload the processing required by a system centralprocessing unit (CPU) 972. This will provide for higher overall systemperformance. In addition, the CMTS MAC 930 is able to provide supportfor carrier class redundancy via timestamp synchronization across anumber of receivers, shown as a receiver 911, a receiver 911, and areceiver 913 that are each operable to receive upstream analog inputs.In certain embodiments, each of the receivers 911, 912, and 913 are dualuniversal advanced TDMA/CDMA (Time Division Multiple Access/CodeDivision Multiple Access) PHY-layer burst receivers. That is top say,each of the receivers 911, 912, and 913 includes at least one TDMAreceive channel and at least one CDMA receive channel; in this case,each of the receivers 911, 912, and 913 may be viewed as beingmulti-channel receivers.

[0106] In addition, the CMTS MAC 930 may be operated remotely with arouting/classification engine 979 that is located externally to the CMTSMAC 930 for distributed CMTS applications including mini fiber nodeapplications. Moreover, a Standard Programming Interface (SPI) masterport may be employed to control the interface to the receivers 911, 912,and 913 as well as to a downstream modulator 920.

[0107] The CMTS MAC 930 may be viewed as being a highly integrated CMTSMAC integrated circuit (IC) for use within the various DOCSIS andadvanced TDMA/CDMA physical layer (PHY-layer) CMTS products. The CMTSMAC 930 may employ hardware engines for upstream and downstream paths.The upstream processor design is segmented and uses two banks ofSynchronous Dynamic Random Access Memory (SDRAM) to minimize latency oninternal buses. The two banks of SDRAM used by the upstream processorare shown as upstream SDRAM 975 (operable to support keys andreassembly) and SDRAM 976 (operable to support Packaging, Handling, andStorage (PHS) and output queues). The upstream processor performs DataEncryption Standard (DES) decryption, fragment reassembly,de-concatenation, payload packet expansion, packet acceleration,upstream Management Information Base (MIB) statistic gathering, andpriority queuing for the resultant packets. Each output queue can beindependently configured to output packets to either a Personal ComputerInterface (PCI) or a Gigabit Media Independent Interface (GMII). DOCSISMAC management messages and bandwidth requests are extracted and queuedseparately from data packets so that they are readily available to thesystem controller.

[0108] The downstream processor accepts packets from priority queues andperforms payload header suppression, DOCSIS header creation, DESencryption, Cyclic Redundancy Check (CRC) and Header Check Sequence (ofthe DOCSIS specification), Moving Pictures Experts Group (MPEG)encapsulation and multiplexing, and timestamp generation on the in-banddata. The CMTS MAC 930 includes an out-of-band generator and TDMAPHY-layer (and/or CDMA PHY-layer) interface so that it may communicatewith a CM device's out-of-band receiver for control of power managementfunctions. The downstream processor will also use SDRAM 977 (operable tosupport PHS and output queues). The CMTS MAC 930 may be configured andmanaged externally via a PCI interface and a PCI bus 971.

[0109] Each of the receivers 911, 912, and 913 is operable to supportinterference cancellation functionality. For example, the receiver 911is operable to support interference cancellation functionality, as shownin a functional block 991; the receiver 912 is operable to supportinterference cancellation functionality, as shown in a functional block992; and the receiver 913 is operable to support interferencecancellation functionality, as shown in a functional block 993. The FIG.9 shows yet another embodiment in which interference cancellation may beperformed according to the present invention. Any of the functionalityand operations described in the other embodiments may be performedwithin the context of the CMTS system 900 without departing from thescope and spirit of the invention.

[0110]FIG. 10 is a system diagram illustrating an embodiment of a burstreceiver system 1000 that is built according to the present invention.The burst receiver system 1000 includes at least one multi-channelreceiver 1010. The multi-channel receiver 1010 is operable to receive anumber of upstream analog inputs that are transmitted from CMs. Theupstream analog inputs may be in the form of either TDMA (Time DivisionMultiple Access) and/or CDMA (Code Division Multiple Access) format. Anumber of receive channels may be included within the multi-channelreceiver 1010.

[0111] For example, the multi-channel receiver 1010 is operable tosupport a number of TDMA receive channels 1020 (shown as TDMA signal 1and TDMA signal 2) and to support interference cancellationfunctionality, as shown in a functional block 1021, for those receivedTDMA signals. The multi-channel receiver 1010 is operable to support anumber of TDMA receive channels 1030 (shown as CDMA signal 1 and CDMAsignal 2) and to support interference cancellation functionality, asshown in a functional block 1031, for those received CDMA signals.Generically speaking, the multi-channel receiver 1010 is operable tosupport a number of receive channels 1040 (shown as received signal 1and received signal 2) and to support interference cancellationfunctionality, as shown in a functional block 1041, for those receivedsignals. The multi-channel receiver 1010 of the FIG. 10 is operable tointerface with a CMTS MAC. The burst receiver system 1000 may include anumber of multi-channel receivers that are each operable to interfacewith the CMTS MAC.

[0112] In certain embodiments, the multi-channel receiver 1010 providesa number of various functionalities. The multi-channel receiver 1010 maybe a universal headend advanced TDMA PHY-layer QPSK/QAM (QuadraturePhase Shift Keying/Quadrature Amplitude Modulation) burst receiver; themulti-channel receiver 1010 also include functionality to be a universalheadend advanced CDMA PHY-layer QPSK/QAM burst receiver; or themulti-channel receiver 1010 also include functionality to be a universalheadend advanced TDMA/CDMA PHY-layer QPSK/QAM burst receiver offeringboth TDMA/CDMA functionality. The multi-channel receiver 1010 may beDOCSIS/EuroDOCSIS based, IEEE 802.14 compliant. The multi-channelreceiver 1010 may be adaptable to numerous programmable demodulationincluding BPSK (Binary Phase Shift Keying), and/or QPSK,8/16/32/64/128/256/516/1024 QAM. The multi-channel receiver 1010 isadaptable to support variable symbols rates as well. Other functionalitymay likewise be included to the multi-channel receiver 1010 withoutdeparting from the scope and spirit of the invention. Such variationsand modifications may be made to the communication receiver.

[0113]FIG. 11 is a system diagram illustrating an embodiment of a singlechip DOCSIS/EuroDOCSIS CM system 1100 that is built according to thepresent invention. The single chip DOCSIS/EuroDOCSIS CM system 1100includes a single chip DOCSIS/EuroDOCSIS CM 1110 that is implemented ina very high level of integration and offering a very high level ofperformance. A coaxial cable in input to a DiPlexer to provide CM accessto the single chip DOCSIS/EuroDOCSIS CM system 600. The DiPlexercommunicatively couples to a CMOS (Complementary Metal OxideSemiconductor) tuner. The CMOS tuner may be implemented with a companionpart that includes a low noise amplifier (LNA) and performs radiofrequency (RF) automatic gain control (AGC). This two part solution isoperable to support 64 and 256 QAM. These two parts operatecooperatively with the single chip DOCSIS/EuroDOCSIS CM 1110. The CMOStuner may be operable to support an intermediate frequency (IF) outputfrequency range of 36-44 MHz, and specifically support the 36.125 and43.75 MHz center frequencies for the Phase Alteration Line (PAL) andNational Television System Committee (NTSC) standards. Also, the CMOStuner and the LNA and RF AGC are DOCSIS and EuroDOCSIS standardsupportable.

[0114] However, it is also noted that the CMOS tuner is operable toperform direct RF to baseband (BB) frequency transformation withoutrequiring the IF transformation. The received signal from the DiPlexer.An external bandpass Surface Acoustic Wave (SAW) filter removes thechannels distant from the desired signal.

[0115] The output from the SAW filter is then passed to the single chipDOCSIS/EuroDOCSIS CM 1110. The single chip DOCSIS/EuroDOCSIS CM 1110 issupported by Synchronous Dynamic Random Access Memory (SDRAM) and Flash.In addition, the single chip DOCSIS/EuroDOCSIS CM 1110 supports bothEthernet and USB interfacing to any other devices that may exist withinthe single chip DOCSIS/EuroDOCSIS CM system 1100. The FIG. 11 shows yetanother embodiment in which interference cancellation may be performedaccording to the present invention. The interference cancellationfunctionality may be supported directly within the single chipDOCSIS/EuroDOCSIS CM 1110. The single chip DOCSIS/EuroDOCSIS CM system1100 shows an application context of yet another implementation of adevice that may perform the present invention.

[0116]FIG. 12 is a system diagram illustrating another embodiment of asingle chip DOCSIS/EuroDOCSIS CM system 1200 that is built according tothe present invention. The single chip DOCSIS/EuroDOCSIS CM system 1200includes a single chip DOCSIS/EuroDOCSIS CM 1210 that combines an RFreceiver with an advanced QAM demodulator, an advanced QAM and S-CDMAmodulator/transmitter, a complete DOCSIS 2.0 Media Access Controller(MAC), a 200 MHz MIPS32 Communication Processor, a 16 bit, 100 MHz SDRAMinterface, 10/100 Ethernet MAC with integrated transceiver and MediaIndependent Interface (MII), and a USB 1.1 controller with integratedtransceiver.

[0117] The QAM receiver directly samples a tuner output (such as theCMOS tuner of the FIG. 6) with an 11 bit analog to digital converter(ADC) and input AGC amplifier. The receiver digitally re-samples anddemodulates the signal with recovered clock and carrier timing, filtersand equalizes the data, and passes soft decisions to an ITU-T J.83 AnnexA/B/C compatible decoder. The receiver supports variable symbol rate4/16/32/64/128/256/1024 QAM Forward Error Correction (FEC) decoding. Thefinal received data stream is delivered in a serial MPEG-2 transportformat. All gain, clock, and carrier, acquisition and tracking loops areintegrated in the QAM receiver.

[0118] The upstream transmitter takes burst or continuous data, providesFEC encoding and pre-equalization for DOCSIS applications, filters andapplies 2/4/8/16/64/256 QAM or S-CDMA modulation to the data stream,amplifies the signal through the integrated upstream power amplifier andprovides a direct 0-65 MHz analog output.

[0119] The MAC of the single chip DOCSIS/EuroDOCSIS CM 1210 includes allfeatures required for full DOCSIS 1.0, 1.1, and 2.0 compliance,including full support for baseline privacy (BPI+) encryption anddecryption. Single-user support includes four SIDS (StandardInteroperable Datalink System) in downstream, four DA perfect matchfilters, a 256 entry CAM for multicast/unicast hash filter and fourindependent upstream queues for simultaneous support of Quality ofService (QoS) and BE traffic. To enhance operational support, the MAC ofthe MAC of the single chip DOCSIS/EuroDOCSIS CM 1210 provides extendedNetwork Management MIB/Diagnostic features, as well as immediate UCC (onthe fly) using independent resets for downstream and upstream queues andboth individual queue reset/flush for upstream queues. The MAC of thesingle chip DOCSIS/EuroDOCSIS CM 1210 uses advance PROPANE techniques toprovide packet acceleration to significantly improve upstream channelutilization.

[0120] With the incorporation of an upstream power amplifier, the MAC ofthe single chip DOCSIS/EuroDOCSIS CM 1210 allows a complete CM to beassembled with a minimal set of external components. When used with aCMOS tuner, such as the CMOS tuner of the FIG. 11, a very low costsolution for a high performance, single user DOCSIS 2.0 CM is provided.The MAC of the single chip DOCSIS/EuroDOCSIS CM 1210 of the FIG. 12 isoperable to support all digital reference frequency lockingfunctionality according to the present invention. The FIG. 12 shows yetanother embodiment where interference cancellation functionality may besupported according to the present invention. The interferencecancellation functionality may be viewed as being supported andperformed within the DOCSIS 2.0 MAC of the single chip DOCSIS/EuroDOCSISCM 1210 of the FIG. 12.

[0121]FIG. 13 is a system diagram illustrating an embodiment of a singlechip wireless modem system 1300 that is built according to the presentinvention. The single chip wireless modem system 1300 includes a singlechip wireless modem 1310 that is operable to support a variety offunctionalities. The single chip wireless modem system 1300 is operableto perform wireless LAN operation using an 802.11 radio that is operableto communicatively couple to an external device that is wireless capable(example shown as the pen computer having wireless functionality). Thesingle chip wireless modem 1310 of the single chip wireless modem system1300 employs a 10/100 Ethernet PHY and an HPNA (Home Phoneline NetworkAlliance) analog front end (AFE) that is operable to interface with theHPNA 2.0 network. The single chip wireless modem 1310 of the single chipwireless modem system 1300 also supports capability to communicate withan external device via a USB 1.1 interface.

[0122] The single chip wireless modem 1310 of the single chip wirelessmodem system 1300 is compatible with existing cable modem applicationcode. In addition, the single chip wireless modem 1310 supports advancedQAMLink® modulation/demodulation TP provide for higher throughputs andperformance in noisy plant environments. The 802.11b MAC and basebandallow for wireless connectivity as mentioned above. In addition, theintegrated HPNA 2.0 MAC supports high-speed multimedia services overphone lines. The integrated 10/100 Ethernet and USB 1.1 with integratedtransceiver provide for a low cost CPE (Customer Premises Equipment),and the MPI interfaces provide for great flexibility through additionalconnectivity options. The single chip wireless modem 1310 is a part of acomprehensive solution that is operable to support certifiableDOCSIS/EuroDOCSIS 1.1 software as well as supporting residential gatewaysoftware including Firewall, NAT and DHCP. The FIG. 13 shows yet anotherembodiment where interference cancellation functionality may besupported according to the present invention. The interferencecancellation functionality may be viewed as being supported andperformed within the single chip wireless modem 1310 of the single chipwireless modem system 1300.

[0123]FIG. 14 is a system diagram illustrating another embodiment of asingle chip wireless modem system 1400 that is built according to thepresent invention. The single chip wireless modem system 1400 includes asingle chip wireless modem that is operable to support a variety offunctionalities. The single chip wireless modem of the single chipwireless modem system 1300 integrates the DOCSIS/EuroDOCSIS 2.0 cablebased modem with a 2/416/32/64/128/256/1024 QAM downstream receiver withAnnex A, B, C FEC support. In addition, the single chip wireless modemintegrates the DOCSIS/EuroDOCSIS 2.0 cable based modem with2/4/8/16/32/64/128/256 QAM FA-TDMA ad S-CDMA. The 802.11b wireless MACand baseband are also integrated on the single chip wireless modem. Anumber of other functional blocks are also integrated thereon,including, a 300 MHz MIPS32 CPU, a 32 bit 100 MHz SDRAM/DDR controller,an integrated upstream amplifier, an integrated IP SEC engine, anintegrated advance PROPANE™ packet accelerator, a 12 Mbps USB 1.1 slaveport with integrated transceiver, a 10/100 Ethernet MAC/PHY with MIIinterface, an MPI expansion bus (that supports PCI, Cardbus, and PCMCIAinterfaces), a single 28 MHz reference crystal, and ability to operateusing voltages of 1.8 V and/or 3.3 V.

[0124] The advanced QAMLink® technology of the single chip wirelessmodem, compliant with DOCSIS 2.0, supports up to 1024 QAM downstreammodulation formats and both FA-TDMA and S-CDMA, with 256 QAM upstreammodulation formats. This advanced technology provides a higherthroughput and superior performance in noise plant environments, pavingthe way for symmetrical services, such as video conferencing.

[0125] The single chip wireless modem integrates both wireless andwireline networking functions for distributing broadband contentthroughout the home. An 802.11b solution is provided for wirelessconnectivity, while both 10/100 Ethernet and 32 Mbps HPNA 2.0 solutionsprovide wired connectivity. HPNA 2.0 allows multimedia services to bestreamed across existing home phone lines.

[0126] The PROPANE™ technology provides bandwidth and performanceenhancements to existing cable plants allowing up to twice as manysubscribers per node, thereby minimizing the need for node splits. TheFIG. 14 shows yet another embodiment where interference cancellationfunctionality may be supported according to the present invention. Theinterference cancellation functionality may be viewed as being supportedand performed within the single chip wireless modem of the single chipwireless modem system 1400.

[0127]FIG. 15 is a diagram illustrating an embodiment of a vectorde-spreader 1500 that is built according to the present invention. Thefollowing description of embodiments of the present invention using theFIGS. 15, 16, 17, and 18 are made within the context of the DOCSIS 2.0system. This system uses S-CDMA modulation for the upstream with 128orthogonal codes. In the example there are 120 active (data-carrying)codes, with 8 unused codes. This example is for illustrative purposesonly, and should by no means limit the scope of the invention. Again, itis noted that the specific examples of 120 active codes, and 8 unusedcodes in a system having 128 available codes is exemplary. Clearly,other embodiments may be employed (having different numbers ofcodes—both different numbers of used and unused) without departing fromthe scope and spirit of the invention.

[0128] The FIG. 15 depicts a vector de-spreader, arranged according tothe present invention, consisting of 128 individual scalar de-spreaders.De-spreading is the process of multiplying by a given code sequence andsumming (or integrating) over many chips, in this case the length of thecode, 128 chips. Each scalar de-spreader performs the function ofde-spreading the received signal (input spread signal to be de-spread)using a single de-spreading code (c₁, c₁₂₈). There are 128 orthogonalde-spreading codes in the present example.

[0129]FIG. 16 is a diagram illustrating an embodiment of an interferencecanceler 1200 that is built according to the present invention. Thespread input signal x, consisting of the sum of multiple spreading codesmodulating multiple data streams, enters the diagram at the left. Theundesired interference n is added to the signal. The signal is appliedto the vector de-spreader, which de-spreads each of the 128 codes. Theupper 8 codes are not used for data transmission and are modulated withnumerically zero-valued symbols instead of data. Clearly, there may beembodiments where other numerically constant-valued symbols may beemployed instead of data as well. Further, the symbol may contain datarepresented as a reduced constellation, such as BPSK or QPSK, on the“unused” codes.

[0130] One of the 120 data-carrying codes, code d_(s), is identified forillustration in the FIG. 16. In order to cancel the interference, thede-spreader output d_(s) is processed in a linear combiner, where it issummed with a linear combination of the 8 de-spreader outputs from thezero-modulation codes d₁-d₈. The complex-valued combining weightsapplied to these codes are w₁-w₈, respectively. These weights arecomputed in a weight computation method as shown in the lower right handcorner of the FIG. 16 using the weight computation functionality.

[0131] The weight computation functionality may employ a method thatutilizes the input spread signal plus interference, and may utilize somesystem outputs if an iterative method is used. Weight computationmethods that have been found valuable are the LMS (least mean square)method and the LS (least squares) method. The result of the linearcombination is the output {circumflex over (d)}_(s), which is the datastream d, with the interference largely removed. Although not shown inthe figure, the same linear combiner structure is applied to the other119 codes as well (all of the other active codes besides the coded_(s)). In each case, the desired code (one of the 120 “active” ordata-carrying codes) is applied to a linear combiner to cancel theinterference from that code. For each data-carrying code, the same 8zero-modulation codes are summed with the desired code, but for eachactive code the weights w₁-w₈ are in general unique.

[0132] An alternative viewpoint is to define the adapted code as${c_{a}(n)} = {{c_{s}(n)} + {\sum\limits_{k = 1}^{N_{\mu}}{w_{k}{c_{k}(n)}}}}$

[0133] that is, the desired code plus the linear combination of theweights times the unused (“inactive”) codes. In this view, the adaptedcode is a modified code with complex coefficients, which is used insteadof the code c_(s) to de-spread a single desired signal from a singlemodulated code, while simultaneously canceling the interference.

[0134] This approach can be extended to matrix notation by defining theadapted code matrix as

C_(adapted)=C_(used)+WC_(unused)

[0135] where:

[0136] C_(adapted)=adapted code matrix, dimension (N_(c)−N_(u))×128, forexample, 120×128

[0137] C_(used)=matrix whose rows are the used codes in the originalcode matrix, dimension (N_(c)−N_(u))×N_(c), for example, 120×128W=matrix whose rows are the adaptive weight vectors for each unusedcode, dimension (N_(c)−N_(u))×N_(u), for example, 120×8

[0138] C_(unused)=matrix whose rows are the unused codes in the originalcode matrix, dimension N_(u)×N_(c), for example, 8×128

[0139] N_(c)=number of total codes=number of chips in each code, forexample, 128

[0140] N_(u)=number of unused codes, for example, 8

[0141] In this view, the adapted code matrix is a modified code matrixwith complex coefficients, which is used instead of the code matrix C tode-spread the desired signals from all used codes, while simultaneouslycanceling the interference on all used codes.

[0142] It is noted that that the unused codes may be de-spread as well,and this side information, though not data-carrying, is of use incharacterizing the interference environment.

[0143] It is also noted that the weight computation functionality may beperformed offline, and these pre-computed complex-valued combiningweights, w₁-w₈, may then be stored in memory and/or a look up table(LUT) that may be used to provide the complex-valued combining weights,w₁-w₈. The appropriate set of weights may be selected after analyzingthe interference environment.

[0144]FIG. 17 is a diagram illustrating another embodiment of aninterference canceler 1700 that is built according to the presentinvention. The FIG. 17 may be viewed as being somewhat similar to theinterference canceler 1600 of the FIG. 16 with some exceptions relatingto the specific codes that are used to perform the linear combination inan effort to perform the interference cancellation according to thepresent invention.

[0145] The FIG. 17 shows an embodiment where all of the codes areincluded in the linear combiner. This includes both the used codes andthe unused codes, instead of only the unused codes. This will be usefulif there is inter-code interference (ICI), since in that case thedesired signal will appear on all codes. Conversely, the signalsmodulated onto all codes will appear on the desired de-spreader output,and can be subtracted from the desired de-spreader output.

[0146] In yet another alternative embodiment, to add to the number ofeffective unused codes, we may use codes bearing preamble symbols inaddition to the codes carrying zero-valued symbols. The preamble symbolsare known and can be subtracted once their amplitude and phase have beenmeasured, for example using a preamble correlator. Thus thepreamble-bearing codes can also be used as inputs to the linear combinerin order to better cancel the interference.

[0147] There are some other embodiments that may be employed as well.For example, the selection of the inactive codes may be performed asfollows: (1) use codes 0, 1, 2, 3, . . . (adjacent codes, as done inDOCSIS 2.0 spec) in which the codes are adjacent and the lower codesused in the coding and/or (2) spacing the codes maximally apart. Forexample, using DOCSIS 2.0 S-CDMA code set, the 8 unused codes out of 128total codes might be code numbers {15 31 47 63 79 95 111 127} whenseeking to perform the maximally spaced apart embodiment. Moreover, theselection of the unused codes may be performed according to anoptimality criterion. Examples of some potential optimality criteriainclude: (1) select unused codes that have maximal correlation with theinterference, (2) minimize enhancement of white noise resulting fromcancellation process, and (3) minimize residual interference power aftercancellation.

[0148] It is also noted that the particular codes that are selected asthe unused codes may change over time during the processing of receivedsignals. Moreover, the particular selection of the codes may vary fromone iteration to the next. For example, in one situation, adjacent codesmay be selected as the unused codes. In another situation, the maximallyspaced codes may be selected as the unused codes.

[0149] The selection of the codes that are to be designated the unusedcodes may be performed using a variety of approaches including: (1)employing code matrix reordering, (2) employing null grant periods, (2)zero padding data, and/or (4) employing some optimality criterion (orcriteria).

[0150] Similar to the embodiment of the FIG. 16, it is also noted thatthe weight computation functionality may be performed offline, and thesepre-computed complex-valued combining weights that are used here in theFIG. 17 may similarly be stored in memory and/or a look up table (LUT)that may be used to provide the complex-valued combining weights. Theappropriate set of weights may be selected after analyzing theinterference environment. This may similarly be performed in theembodiments of the FIGS. 18 and 19 described in further detail belowwhere these pre-computed complex-valued combining weights may also bestored in memory and/or a look up table (LUT).

[0151]FIG. 18 is a diagram illustrating another embodiment of aninterference canceler 1800 that is built according to the presentinvention. The FIG. 18 may be viewed as being a variant of the FIG. 17that has access to any of the codes (including both used and unusedcodes). The FIG. 18 includes a subset of the codes for use in the linearcombiner, instead of all the codes or only the unused codes. Forexample, in DOCSIS 2.0 S-CDMA, adjacent codes are nearly shifts of eachother. When a timing offset occurs, the codes lose orthogonality and ICIoccurs. However, the ICI is predominant on the adjacent codes. Forexample, in the presence of a timing offset, code 35 will be interferedwith predominantly by codes 34 and 36, with lesser effects coming fromcodes 33 and 37, even lesser effects from codes 32 and 38, and so on.Hence including as inputs to the linear combiner the data-bearing codes33, 34, 36 and 37, plus the unused codes, but not the remainingdata-bearing codes, will reduce the number of weights that have to besolved for compared to the more general case above in which all codesare included in the linear combination. Another embodiment would involveincluding as inputs to the linear combiner the data-bearing codes 34,and 36, plus the unused codes, but not the remaining data-bearing codes,in an effort to try to reduce the number of weights that have to besolved for compared to the more general case above in which all codesare included in the linear combination.

[0152]FIG. 19 is a diagram illustrating an embodiment of an interferencecanceler with memory 1900 that is built according to the presentinvention. The FIG. 19 shows an interference canceler with memory, thatis, it uses the history of previous samples in computing the output. Theweight w₁ has been replaced with “feed-forward equalizer 1” (FF Eqer.1), a tapped delay line or FIR filter with L weights. The other adaptiveweights have similarly been replaced with FF equalizers 2-8. It is notedthat both the current and past soft de-spread symbols are included inthe linear combination. Moreover, future soft de-spread symbols may alsobe included in the linear combination; these future soft de-spreadsymbols are “future” relative to the symbol currently being estimated.This permits each tap to have a frequency selective response.

[0153]FIG. 20 is a diagram illustrating an embodiment of equalizationwith canceler 2000 that is arranged according to the present invention.The FIG. 20 may be viewed as being a representation of equalization ofchannel response, and cancellation of resulting colored noise. Thecanceler structure can also be used to help with equalization. The FIG.20 considers a communications system with a transmitter 2010, a channel2020 having a response H(f), and a receiver 2025. Let the channelresponse be H(f). We assume, as an example, that H(f) exhibits a null atsome frequency in the signaling band of interest. Assume AWGN (additivewhite Gaussian noise) is added in the channel after H(f). We may use astandard adaptive equalizer 2030 at the receiver to provide the inverse(zero forcing) response, 1/H(f), which will have a narrow peak at thefrequency location where the null exists in H/(f). This peak will causethe white noise to be colored and to have a peak as well. Thisnarrowband colored noise can be canceled (using the canceler 2040) bythe present technique in exactly the same manner that other narrowbandinterference is canceled. The FIG. 20 shows yet another embodiment ofhow interference cancellation, according to the present invention, maybe performed.

[0154]FIG. 21 is a diagram illustrating an embodiment of Least MeansSquare (LMS) training of an interference canceler 2100 according to thepresent invention. The FIG. 21 may be viewed as being one embodimentthat is operable to perform adaptation of an interference canceler usingiterative methods. The present interference canceler 2100 can be adaptedusing iterative methods such as LMS or RLS. The FIG. 21 illustrates howthe LMS method may be used to adapt the canceler weights. The output ofthe de-spreader for the desired code (containing soft decisions) issliced to produce hard symbol decisions. If known training symbols areavailable, they replace the hard decisions, which may contain symbolerrors, especially upon startup. The difference between the hard (orknown) and soft decisions gives the LMS error sample. The error iscorrelated with the outputs of the unused code de-spreaders and used toupdate the adaptive weights wi.

[0155] Within the FIG. 21, the slicer, the MUX, and the LMS error (andLMS step-size scaling μ) that are used to update the adaptive weights wimay be viewed as being just one embodiment of an iterative, errordetermining approach. Clearly, other error determining approaches(besides LMS) may be employed without departing from the scope andspirit of the invention. The error calculation and correlation with theoutputs of the unused code de-spreaders that are used to update theadaptive weights wi may be viewed as being an iterative adaptive weightfunctionality that may be viewed as being provided in an implementationvia an iterative adaptive weight functional block that communicativelycouples to each of the outputs of the unused code de-spreaders.

[0156]FIG. 22A is a diagram illustrating an embodiment of signaltransformation according to the present invention. The FIG. 22A includesthe pre-processing of an input signal, and unused inputs, via anorthogonal transformation 2210 to generate a representation of the inputsignal within a finite signal space. The orthogonal transformation 2210may be an orthonormal transformation in certain embodiments. Now thatthe input signal is represented in the finite signal space, the signalis then passed through a communication channel 2230 after which it isprovided to an interference cancellation functional block 2220 that isoperable to perform any of the various embodiments of interferencecancellation described herein. The communication channel 2230 mayintroduce interference. It is noted that the present invention isoperable to perform cancellation of interference of a variety of typesincluding (1) narrowband interference in general, (2) Ham radio, CBradio and HF radio, (3) adjacent channel interference (spillover fromdesired signals in neighboring channels), (4) CDMA on a small number ofcodes, and (5) impulse burst note. The present invention envisions anyorthogonal transformation 2210 that is operable to transform an inputsignal into a representation of a finite number of elements within afinite signal space so as to facilitate the interference cancellationaccording to the present invention.

[0157]FIG. 22B is a diagram illustrating another embodiment of signaltransformation according to the present invention. The FIG. 22B includesthe pre-processing of an input signal, and unused inputs, via anidentity matrix transformation 2215 to generate a representation of theinput signal within a finite signal space. Again, the orthogonaltransformation 2215 may be an orthonormal transformation in certainembodiments. Now that the input signal is represented in the finitesignal space, the signal is then passed through a communication channel2235 after which it is provided to an interference cancellationfunctional block 2225 that is operable to perform any of the variousembodiments of interference cancellation described herein. Thecommunication channel 2235 may introduce interference. It is again notedthat the present invention is operable to perform cancellation ofinterference of a variety of types including (1) narrowband interferencein general, (2) Ham radio, CB radio and HF radio, (3) adjacent channelinterference (spillover from desired signals in neighboring channels),(4) CDMA on a small number of codes, and (5) impulse burst note. Furtherdetails are described below with respect to impulse noise cancellation.

[0158] Impulse noise is nearly zero most of the time, and large during afew samples. For the purpose of analysis only, we consider the rows ofthe N×N identity matrix as the basis set, where N is the number ofsamples per frame (or chips per spreading interval) under consideration.In this basis set, each time sample is a dimension. Hence we see thatthe impulse noise only occupies a small number of dimensions. Thus itcan be canceled by this technique, using an arbitrary basis set, such asthe S-CDMA codes. The adapted de-spreading code has zeros (or nearlyzeros) at the chips corresponding to the time location of the impulsenoise. However, impulse noise occurs at a random, unpredictable locationin each frame. If we know where it is, we can solve the equations forthe weights. But the next frame it will be in a different place. Thismeans re-doing the computations every frame, resulting in highcomplexity.

[0159] For low-level impulse noise, it may be difficult to locate thechips that are affected by impulse noise. We may use one or more“indicator codes” for this purpose, as follows. As an example, say wehave 128 total codes—for example in the DOCSIS 2.0 situation. Wedesignate 119 of these codes as used, or data-carrying codes. Wedesignate 9 of the codes as unused codes, on whichnumerically-zero-valued symbols are transmitted. Of these 9 unusedcodes, 8 codes participate in the linear combiner for noisecancellation, and there is 1 extra or “indicator” code. The indicatorcode is de-spread as if it were a used code, that is, it is given thebenefit of the linear combiner canceler. We expect to get a zero symbolat its de-spreader output; if we see noise instead of zero that providesan indication of the amount of noise that has not been canceled. We thenproceed as follows to locate the impulse noise. Assume for example thatthere is one occurrence of impulse noise in a given symbol, and that theimpulse noise affects 8 or fewer chips. We begin with a set of weights wthat null chips 1 through 8 in the time domain. We use w to de-spreadthe indicator code, and observe the output y. We then modify w to nullchips 2-9, and again observe y. In a similar manner, we scan w acrossthe entire symbol, measuring y at each time offset. We believe, but havenot yet demonstrated, that the power |Y|² will exhibit a minimum for theweight set w that corresponds to the time location of the impulse noise.In this manner the location of the impulse noise can be determined. Oncelocated, it can be canceled.

[0160]FIG. 23 is an operational flow diagram illustrating an embodimentof an interference cancellation method 2300 that is performed accordingto the present invention. In a block 2310, a spread signal is receivedthat contains interference. Then, the received spread signal isde-spread into a number of codes in a block 2320. Each of the codes isselectively processed using linear combination processing as shown in ablock 2330. There are a variety of ways in which the linear combinationprocessing may be performed according to the present invention includingusing a number of unused codes, using all of the available codes, and/orusing selected adjacent codes in addition to the unused codes.Ultimately, the interference cancelled de-spread codes are output asshown in a block 2340.

[0161]FIG. 24 is an operational flow diagram illustrating anotherembodiment of an interference cancellation method 2400 that is performedaccording to the present invention. Initially, in some embodiments, themethod involves selecting those codes that are to be used as the unusedcodes as shown in a block 2402. As shown within the FIG. 24, there arethree different ways in which this may be performed. They include codematrix reordering, employing null grant periods, and/or zero paddingdata. Even other ways are described when referring to the other Figuresas well. These will be the codes that are used to perform the linearcombining to effectuate the interference cancellation according to thepresent invention. In even other embodiments as shown in a block 2404,the unused codes (N_(u)) are modulated with numerically zero-valuedsymbols. Alternatively, the unused codes (N_(u)) may be modulated withnumerically constant-valued symbols that are non-zero without departingfrom the scope and spirit of the invention.

[0162] In a block 2410, a spread signal is received that containsinterference. Then, the received spread signal is de-spread into anumber of codes (N_(c)) as shown in a block 2420. in a block 2430, eachof the number of unused codes (N_(u)) is selectively de-spread. Themethod then will continue to the block 2440 in most instances.

[0163] However, in certain embodiments, the method will continue fromthe block 2430 to the block 2432 in which each of the number of preamblecodes is selectively de-spread. The preamble symbols are known and canbe subtracted once their amplitude and phase have been measured, asshown in a block 2434, for example using a preamble correlator. Thus thepreamble-bearing codes can also be used as inputs to the linear combinerin order to better cancel the interference.

[0164] As shown in the block 2440, complex-valued weights for linearcombination processing of the unused codes (N_(u)) are selectivelycalculated. This processing in the block 2440 may be performed byinputting the spread signal, interference, and/or outputs as shown in ablock 2442. In the embodiments where the blocks 2432 and 2434 areperformed, the preamble-bearing codes may be input as shown in a block2444 when performing the processing in the block 2440. The processing inthe block 2440 may be performed be employing LMS processing as shown ina block 2446 and/or LS processing as shown in a block 2448.

[0165] Then, in a block 2450, the complex value weights are selectivelyapplied to scale the unused codes (N_(u)). In a block 2460, the nowscaled unused codes (N_(u)) are selectively summed with the desiredcode. Ultimately, the interference cancelled de-spread codes are outputas shown in a block 2440.

[0166]FIG. 25 is an operational flow diagram illustrating an embodimentof an unused code selection method 2500 that is performed according tothe present invention. The question sometimes arises whether any subsetof the codes is a good choice for the unused codes. We consider theexample of narrowband interference cancellation in a DOCSIS 2.0 S-CDMAsystem. For efficient narrowband interference canceling capability, theunused codes have to be chosen such that it is possible to combine themin the adapted codes (in the linear combiner) to form one or morenotches in the frequency domain. Thus, for optimal performance, onemight need to designate specific codes as unused. The current DOCSIS 2.0draft specification does not permit the selection of which codes areunused. It has been found that successive, or “adjacent”, DOCSIS 2.0codes are not a good choice. This is because each code is approximatelya shift of the previous code. This implies that adjacent or nearlyadjacent codes have nearly the same frequency response. Some techniquesthat could be used to “force” unused codes at specific rows of the codematrix are the following:

[0167] The code matrix may be reordered. In this technique, both the CMand CMTS re-order the code matrix as shown in a block 2510, prior tospreading or de-spreading. This may be performed such that desiredunused codes are grouped together (say at the lower part of therearranged code matrix) as shown in a block 2520. Similarly, the desiredused codes should be grouped as well (say at the upper part of therearranged code matrix) as shown in a block 2530. Using such techniquerequires the knowledge of the reordering pattern at the CMTS as well asall CMs; this may be ensured as shown in a block 2540.

[0168] Alternatively, the selection of unused codes may be performedusing null grant periods. In this technique, the CMTS instructs all CMsto be silent during a specific grant as shown in a block 2505 (i.e., thedesired unused codes). This technique has the advantage that the CMsneed not have prior knowledge of the unused codes and just follow theCMTS grants. However, it may be viewed as causing inefficiencies to theCMTS scheduling process that may prohibit this approach in someimplementations.

[0169] Alternatively, the selection of unused codes may be performed byzero-padding the data. In this technique, the CMTS grants the CM alonger grant period that what is needed to transmit the grant data asshown in a block 2555. If desired when performing the operation of theblock 2555, the grant sizes are chosen by the CMTS in a way such thatthe CM zero-padding occurs at the desired unused codes as shown in ablock 2557. The CMTS also instructs the CM to append the transmitteddata with zero-symbols as shown in a block 2565.

[0170]FIG. 26 is an operational flow diagram illustrating an embodimentof an S-CDMA interference cancellation method 2600 that is performedaccording to the present invention. In a block 2610, a set of used codesis selected. Then, in a block 2620, a set of unused codes is selected. Asignal is transmitted using the used codes as shown in a block 2630. Incertain embodiments, as shown in a block 2632, we transmit one or morezeroes on the inactive/unused codes. Alternatively, as shown in a block2634, we transmit a known sequence (training or pilot symbols) on theinactive/unused codes. Alternatively, we may transmit lower ordermodulation on “inactive” codes.

[0171] Then, in a block 2640, the received signal is processed using thereceived signal's projection on the active (used) codes and the inactive(unused) codes thereby canceling interference. We process the receivedsignal using both its projection onto a desired (active) code, and itsprojection onto the inactive codes, in order to cancel interference onthe desired code. From certain perspectives, in the context of a systemand method that employ vector de-spreading to a spread signal, theprojection may be viewed as being the vector de-spreader output.However, in other contexts, a projection may be viewed as being therepresentation of the received signal across its finite signal space.This understanding of projection may be used to describe therepresentation of the signal across a finite signal space.

[0172] The FIG. 26 is performed within the context of an S-CDMAcommunications system in the presence of interference. There are anumber of types of S-CDMA systems that may support the method of theFIG. 26. For example, some types of S-CDMA systems include DOCSIS 2.0set of codes and Walsh-Hadamard codes. The selection of theinactive/unused codes may be performs as illustrated and described abovewithin some of the embodiments shown in a block 2621 including use codes0, 1, 2, 3, . . . (adjacent codes, as done in DOCSIS 2.0 spec), spacingthe inactive/unused codes maximally apart as shown in a block 2622, andselecting the codes according to an optimality criterion as shown in ablock 2623.

[0173] For example, when spacing the inactive/unused codes maximallyapart within DOCSIS 2.0 S-CDMA code set, the 8 unused codes out of 128total codes might be code numbers {15 31 47 63 79 95 111 127}. Whenselecting a different number of unused codes within the DOCSIS 2.0S-CDMA code set, they may be similarly maximally spaced apart.

[0174] In addition, the inactive/unused codes may be selected accordingto the optimality criterion of the block 2623. Examples of an optimalitycriteria would be to select unused codes include: (1) selectinginactive/unused codes that have maximal correlation with theinterference as shown in a block 2624, (2) minimizing enhancement ofwhite noise resulting from cancellation process as shown in a block2625, and (3) minimizing residual interference power after cancellationas shown in a block 2626.

[0175]FIG. 27 is an operational flow diagram illustrating anotherembodiment of an interference cancellation method 2700 that is performedaccording to the present invention. In a block 2710, a set ofactive/used basis waveforms is selected. These basis waveforms mayinclude orthogonal (or nearly orthogonal) waveforms; these waveforms maybe viewed as being substantially orthogonal. There are a number of typesof sets of orthogonal waveforms may be employed. Some specific examplesof sets of orthogonal waveforms include: (1) S-CDMA codes, includingDOCSIS 2.0 and Walsh-Hadamard, (2) Any orthogonal set of binaryspreading codes, (3) any orthogonal set of quaternary spreading codes,(4) the rows of the identity matrix, and (5) the rows of any unitarymatrix.

[0176] Then, in a block 2720, a set of inactive/unused basis waveformsis selected. In certain embodiments as shown in a block 2722, we mayassume number of inactive/unused basis waveforms is less than number ofactive/used basis waveforms. A signal is transmitted using theactive/used basis waveforms as shown in a block 2730. In certainembodiments, as shown in a block 2732, we transmit one or more zerovalued symbols on the inactive/unused basis waveforms. Alternatively, asshown in a block 2734, we transmit a known sequence (training or pilotsymbols) on the inactive/unused basis waveforms.

[0177] Then, in a block 2740, the received signal is processed using thereceived signal's projection on the active (used) basis waveforms andthe inactive (unused) basis waveforms thereby canceling interference. Weprocess the received signal using both its projection onto a desired(active) waveform, and its projection onto the inactive waveforms, inorder to cancel interference on the desired waveform.

[0178] Alternatively, in a block 2742, the received signal is processedusing the received signal's projection on the active (used) basiswaveforms thereby canceling interference. We process the received signalusing its projection onto a desired (active) waveform in order to cancelinterference on the desired waveform.

[0179] In even alternative embodiments, in a block 2744, we compute theprojection of the interference on the inactive/unused basis waveforms,and subtract it from the projection on the active/used basis waveformsof the received signal including interference thereby cancelinginterference. It is noted here that we can reduce the computationalcomplexity by computing the null-space projection (the projection of theinterference on the inactive basis waveforms) and subtracting it fromthe overall projection (the projection of the signal+interference on theactive basis waveforms). As an example, if we have 120 active codes and8 inactive codes, in the present method we only need to invert an 8×8matrix. In the standard least-squares approach, we would have to inverta 120×120 matrix.

[0180] The selection of the inactive/unused basis waveforms may beperformed as illustrated and described above within some of theembodiments selecting adjacent basis waveforms, spacing theinactive/unused basis waveforms maximally apart, and selecting the basiswaveforms according to an optimality criterion. Examples of anoptimality criteria would be to select unused basis waveforms include:(1) selecting inactive/unused basis waveforms that have maximalcorrelation with the interference, (2) minimizing enhancement of whitenoise resulting from cancellation process, and (3) minimizing residualinterference power after cancellation. These parameters that may be usedto perform the selection of the inactive/unused basis waveforms isanalogous to the selection of the inactive/unused codes that isperformed above with respect to the FIG. 26, except here, the selectionif with respect to the basis waveforms of the signal space.

[0181]FIG. 28 is a diagram illustrating an embodiment of a spectrum ofnarrowband interference 2600 that may be addressed and overcome whenpracticing via the present invention. The FIG. 28 shows the spectrum ofnarrowband interference (for example, the signal n in the FIG. 16, 17,and/or 18) that may be present at the input of a communicationsreceiver. The desired signal is not present in this Figure. In thisexample, the 3-dB bandwidth of the interference is {fraction (1/32)} ofthe symbol rate of the desired signal. Its power is equal to the desiredsignal (0 dBc), when the desired signal is present. The SNR (Signal toNoise) of the desired signal, when present, is 35 dB in the example.

[0182]FIG. 29 is a diagram illustrating an embodiment of a spectrum ofadapted code showing null at a location of interference 2900 that may beachieved when practicing via the present invention. The FIG. 29 showsthe spectrum of the adapted code. The adapted code is seen to have anull corresponding to the narrowband interference. Hence, the adaptedcode cancels the narrowband interference.

[0183]FIG. 30A is a diagram illustrating an embodiment of a receivedconstellation before interference has been cancelled 3000 whenpracticing via the present invention. The FIG. 30A shows the outputd_(s) of the vector de-spreader before interference cancellation isenabled using the linear combiner and weight computation functionality.This may be viewed as being the output d_(s) within any of the FIG. 16,17, and/or 18. That is, all the adaptive weights wi are zero, and onlythe normal de-spreading code c_(s) is used to de-spread the desiredsignal. We see that the signal constellation is unrecognizable due tothe large amount of interference, which has not yet been canceled.

[0184]FIG. 30B a diagram illustrating an embodiment of a receivedconstellation after interference has been cancelled 3005 when practicingvia the present invention. The FIG. 30B shows the output d_(s) of thede-spreader after the interference cancellation of the present inventionis enabled using the linear combiner and weight computationfunctionality. Now the adaptive weights wi have adapted and are nonzero,and as a result the adapted de-spreading code c_(u) is used to de-spreadthe desired signal. We see that the 64 QAM signal constellation, plusthe QPSK constellation used for the preamble, is now clearlyrecognizable and the interference has been effectively canceled.

[0185] Another variant embodiment of the present invention may beperformed by applying the linear combiner at the chip level instead ofthe de-spread symbol level. In this approach, the 128 chips (again usingthe 128 code embodiment example) used in the de-spreader for the desiredcode are adapted (for example, using the LMS method or LS method) untilthey converge to the near-optimal adapted de-spreading code. Thisadapted de-spreading code will be complex-valued and will be a linearcombination of all 128 de-spreading codes. In this approach there are128 adaptive complex weights that need to be trained, so convergence isslower than for the baseline approach in which, for example, only 8weights need to be trained for the 8 unused codes.

[0186] The general applicability of the present invention across a widevariety of contexts is to be understood. The present invention isoperable to cancel not only narrowband interference, but anyinterference that occupies a small number of dimensions in the signalspace. The first example, given above, is narrowband interference.However, other types of narrowband interference may be substantiallyeliminated according to the present invention as well. A narrowbandsignal occupies a small number of DFT bins (DFT: discrete Fouriertransform—one example of an orthonormal expansion) bins, showing that itoccupies a small number of dimensions in signal space.

[0187] An extremely simple example is a CW (Continuous Wave) signalwhose frequency is an integer multiple of the de-spread symbol rate;this CW signal occupies only a single bin in the DFT, or only onedimension in the signal space, where each dimension is, in this case,one DFT bin. Another example is a short burst of noise (impulse or burstnoise). A short burst signal occupies a small number of time samples,again showing that it too occupies a small number of dimensions, whereeach dimension is, in this case, a time sample. Other types of signalscan be constructed without limit that satisfy the property that theyoccupy a small number of dimensions. All such signals can be canceled bythe present technique.

[0188] Again, the DFT is just one example of an orthonormal expansion. Asecond example is the code matrix in DOCSIS 2.0 S-CDMA. Innumerableother orthonormal transforms exist. If a signal occupies a small numberof dimensions in any orthonormal transform, the present invention'stechnique will help cancel it.

[0189] The present invention may also be implemented to use unusedspatial dimensions to cancel interference according to the presentinvention. For example, we can generalize the technique to spatialdimensions as well. One such interpretation of spatial dimensions iswith respect to MIMO (multi-input multi-output) systems. We maydesignate certain transmit antennas to transmit zeros at certain times.At the receiver, we may also utilize the samples from extra receiveantennas to cancel interference.

[0190] In any of the embodiments described herein, the present inventionis operable to store pre-computed weights using any number of variousstorage techniques, such as a look up table (LUT), memory, or some otherstorage technique. This may be beneficial in some cases where it may beimpractical to compute the weights fast enough, so we may want topre-compute some “canned” sets of weights. As an example, consider verywideband interference that occupies {fraction (1/2)} the bandwidth ofthe desired signal. Assuming an S-CDMA system, we will need to have 64unused codes out of 128 total codes. Each desired code now has 64adaptive weights that need to be solved for. This implies a very largematrix to invert, which is very complex to implement in real time.However, we note that in our favor, there are very few notches of thissize (half the bandwidth) to go across the band. If, for example, wepre-compute the weights for several wideband notches and store theweight sets, then we can simply select the notch that most closelymatches the interference when it occurs.

[0191] The present invention is also operable to support adjusting andtracking of pre-computed weights. As an extension to the above conceptof storing pre-computed weights, we may store a single prototype set ofweights, and modify the weights to move the notch around. For example,we can adjust the frequency of the notch without having to completelyre-compute the weights. We can also adjust the depth of the notch. Wecan weight and superimpose pre-computed notches to build up a morecomplex notch structure. We can build a tracking loop that automaticallyadjusts the frequency (or other parameter) of the notch as theinterference changes. Say there is narrowband interference, and we haveapplied a notch that cancels it. Now let the interference slew itsfrequency. We can implement a tracking loop that automatically slews thefrequency location of the notch to track the frequency of theinterference. There are many ways to implement such a tracking loop. Oneway is by taking an FFT of the interference, and tracking the energy inthe peak corresponding to the interference. Another way is to dither thelocation of the notch, and measure the power or SNR at the output. Wethen move the notch in the direction of increasing SNR or decreasinginterference or total power. Many other tracking methods can be devised.

[0192] The present invention may also be implemented to perform adjacentchannel interference (ACI) cancellation when performing interferencecancellation. For example, the canceler can also be used to cancel ACI.Consider a desired signal with signals present in the upper and loweradjacent channels. If the adjacent channel signals overlap slightly withthe desired-signal band, ACI results. ACI is in general colored and cantherefore be canceled using the present canceler technique.

[0193] In performing the processing, the present invention may employ asliding window. The processing has thus far been described as being doneon a block basis, where a block is typically a symbol of 128 chips inthe DOCSIS 2.0 implementation. However, the present invention is alsooperable when employing a sliding block approach as well. This may havethe greatest benefit when the code matrix is the identity matrix, whereno spreading occurs.

[0194] Code hopping is defined in the DOCSIS 2.0 spec as a processwhereby the code matrix is modified by a cyclic rotation of the rows ofthe entire code matrix (except possibly the all—1's code) on eachspreading interval. This causes the set of unused codes to be differenton each spreading interval, requiring the re-computation of the adaptiveweights in the canceler on each spreading interval. It would be betterto hop over the set of codes excluding the unused codes, so that theunused codes will be the same on each spreading interval. This wouldobviate the need to re-computation of the adaptive weights on eachspreading interval, reducing processing complexity. Or, we can just turnoff code hopping when the canceler is used. However, this latterapproach removes the benefits of code hopping, which include fairness(equality of average performance) for all users.

[0195] In the case of the DOCSIS 2.0 S-CDMA code matrix, the rows, orbasis functions, are nearly cyclic shifts of each other, with theexception of code 0. This property relates adjacent codes to shifts intime by one chip. This in turn relates the linear combiner used on thede-spreader outputs to a FIR filter in the time domain. This impliesthat the adaptive weights for the unused codes are similar to theweights that are produced by the time domain interference cancellationstructure used for TDMA. The latter weights can be computed efficientlyby the Trench method. Hence we might use the Trench method to compute aninitial set of weights for the subspace-based canceler, and iterate theweights to a more exact solution using the LMS or similar trackingmethod.

[0196] In addition, a decision feedback equalizer (DFE)-like structuremay also be performed, as follows. The canceler begins by using thede-spreader outputs of codes 1-8 (for example) in the linear combiner toestimate the output of the code 9 de-spreader. A hard decision is madeon the symbol from code 9. Now that the symbol on code 9 is available,it can be used to estimate the symbol on code 10. Once the symbol oncode 10 is available, it can be used to estimate the symbol on code 11,and so on. A DFE-like structure can be constructed that can run in bothdirections.

[0197] As mentioned and described above, the subspace canceler can beapplied to an arbitrary code matrix (basis set). One such basis set isthe discrete Fourier transform (DFT). In this context one should alsomention the fast DFT methods collectively referred to as the fastFourier transform (FFT). The DFT is not well suited for narrowbandinterference cancellation in the receiver without modifications to thecancellation approach. This is because each basis function, the complextone e^(jnω)(or alternatively written as exp(jnω)), is designed to haveminimal support in the frequency domain. The basis functions cannotcancel a narrowband interferer without very large weights. Instead,locating the canceler predominantly in the transmitter is a betterchoice. One simply does not transmit those tones that overlap with theinterference, designating them as unused “codes” or tones. This approachhas been known in the industry for some time in conjunction withdiscrete multi-tone (DMT) or orthogonal frequency division multiplexing(OFDM) systems.

[0198] Moreover, the subspace canceler can be integrated with FECcoding. In one approach, a Reed-Solomon code can provide parity symbolsthat are transmitted on the unused spreading codes instead of zerosymbols. In another approach, different SNRs may exist on differentspreading codes (for example, when spreading code hopping is turnedoff). In this case unequal transmitted power may be sent on eachspreading code, or unequal numbers of bits per symbol of modulation. Or,unequal coding strength can be used on each spreading code: for example,rate ⅞ on one spreading code and rate ¾ on another spreading code. Animportant point is that these approaches will give a better result thancode hopping. In code hopping, performance is averaged over allspreading codes. It is better to use our prior knowledge of whichspreading codes are disadvantaged, and give them more processing poweror transmit power.

[0199] The present invention is also operable, when performinginterference cancellation, to perform adjustment of transmitted spectrumto meet a desired spectral mask. It may be desirable to attenuatecertain portions of the spectrum using the subspace canceler. In theseapplications the canceler is predominantly located in the transmitter.One example is in a wireless local area network (LAN) applications. Hereone has to place a notch in the transmit spectrum at the spectrallocation of the XM satellite radio service. The subspace canceler has agreat advantage over a notch filter. A notch filter can notch out adesignated spectral region, but in doing so, it distorts the desiredsignal. The subspace canceler can create the notch without distortingthe desired signal. The subspace canceler may also have the followingadvantage over a notch filter. A notch filter can cause large excursionsin the transmitted power, whereas the subspace canceler does not.

[0200] The interference cancellation according to the present inventionmay also be integrated with pre-coding. The subspace canceler can beintegrated with pre-coding, such as Tomlinson-Harashima pre-coding. Wenote that the subspace canceler can be used for narrowband interferencecancellation and also for equalization of a deep notch in the channel.These are two applications of pre-coding. Hence, if subspacecancellation and pre-coding were combined, would we get some of theadvantages of both.

[0201] In view of the above detailed description of the invention andassociated drawings, other modifications and variations will now becomeapparent. It should also be apparent that such other modifications andvariations may be effected without departing from the spirit and scopeof the invention.

What is claimed is:
 1. A communication system that is operable toperform interference cancellation, comprising: a transmitter thatproduces a spread signal that comprises a numerically constant-valuedsymbol spread across a first plurality of codes and data spread across asecond plurality of codes and transmits the spread signal across acommunication link; a receiver, communicatively coupled to thetransmitter via the communication link, that receives the spread signalafter being transmitted across the communication link, the spread signalcomprising interference, the receiver comprising: a vector de-spreaderthat de-spreads the first plurality of codes and the second plurality ofcodes from the spread signal; a weight computation functional block thatcalculates a plurality of complex-valued combining weights using thespread signal and the interference of the spread signal; and a linearcombiner that scales the de-spread first plurality of codes using theplurality of complex-valued combining weights and combines the scaled,de-spread first plurality of codes and one code selected from thede-spread second plurality of codes to perform interference cancellationon at least one code de-spread from the spread signal.
 2. Thecommunication system of claim 1, wherein the first plurality of codescomprises a plurality of unused codes; and the second plurality of codescomprises a plurality of used codes.
 3. The communication system ofclaim 2, wherein the first plurality of codes and the second pluralityof codes comprise a total number of 128 codes; the first plurality ofcodes comprises at least 8 codes and no more than 32 codes; the secondplurality of codes comprises a remaining plurality of codes within thetotal number of 128 codes not included within the first plurality ofcodes; and the communication system comprises a DOCSIS 2.0 S-CDMAoperable communication system.
 4. The communication system of claim 1,wherein the weight computation functional block calculates the pluralityof complex-valued combining weights using both the de-spread firstplurality of codes and the de-spread second plurality of codes.
 5. Thecommunication system of claim 1, wherein the weight computationfunctional block calculates the plurality of complex-valued combiningweights using de-spread codes that are adjacent to the one code selectedfrom the de-spread second plurality of codes.
 6. The communicationsystem of claim 5, wherein the adjacent codes comprise two codesimmediately adjacent to the one code selected from the de-spread secondplurality of codes.
 7. The communication system of claim 1, wherein theweight computation functional block calculates the plurality ofcomplex-valued combining weights using de-spread codes from at least oneof the first plurality of codes and the second plurality of codes thatbears preamble symbols.
 8. The communication system of claim 1, whereinthe weight computation functional block employs at least one of leastmeans square processing and least square processing to calculate theplurality of complex-valued combining weights.
 9. The communicationsystem of claim 1, wherein the receiver is operable to demodulate thespread signal using at least one of Binary Phase Shift Keying (BPSK),Quadrature Phase Shift Keying (QPSK), 8 Quadrature Amplitude Modulation(QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and 1024 QAM.10. The communication system of claim 1, wherein the receiver comprisesat least one of a multi-channel headend physical layer burst receiver, asingle chip wireless modem, a single chip DOCSIS/EuroDOCSIS cable modem,a base station receiver, a mobile receiver, a satellite earth station, atower receiver, a high definition television set top box receiver, and atransceiver.
 11. A communication receiver that is operable to performinterference cancellation, comprising: a vector de-spreader thatde-spreads the first plurality of codes and the second plurality ofcodes from a spread signal, the spread signal comprising interference; aweight computation functional block that calculates a plurality ofcomplex-valued combining weights using the spread signal and theinterference of the spread signal; and a linear combiner that scales thede-spread first plurality of codes using the plurality of complex-valuedcombining weights and combines the scaled, de-spread first plurality ofcodes and one code selected from the de-spread second plurality of codesto perform interference cancellation on at least one code de-spread fromthe spread signal.
 12. The communication receiver of claim 11, whereinthe first plurality of codes comprises a plurality of unused codes; andthe second plurality of codes comprises a plurality of used codes. 13.The communication receiver of claim 12, wherein the first plurality ofcodes and the second plurality of codes comprise a total number of 128codes; the first plurality of codes comprises at least 8 codes and nomore than 32 codes; the second plurality of codes comprises a remainingplurality of codes within the total number of 128 codes not includedwithin the first plurality of codes; and the communication systemcomprises a DOCSIS 2.0 S-CDMA operable communication system.
 14. Thecommunication receiver of claim 11, wherein the weight computationfunctional block calculates the plurality of complex-valued combiningweights using both the de-spread first plurality of codes and thede-spread second plurality of codes.
 15. The communication receiver ofclaim 11, wherein the weight computation functional block calculates theplurality of complex-valued combining weights using de-spread codes thatare adjacent to the one code selected from the de-spread secondplurality of codes.
 16. The communication receiver of claim 15, whereinthe adjacent codes comprise two codes immediately adjacent to the onecode selected from the de-spread second plurality of codes.
 17. Thecommunication receiver of claim 11, wherein the weight computationfunctional block calculates the plurality of complex-valued combiningweights using de-spread codes from at least one of the first pluralityof codes and the second plurality of codes that bears preamble symbols.18. The communication receiver of claim 11, wherein the weightcomputation functional block employs at least one of least means squareprocessing and least square processing to calculate the plurality ofcomplex-valued combining weights.
 19. The communication receiver ofclaim 11, wherein the communication receiver is operable to demodulatethe spread signal using at least one of Binary Phase Shift Keying(BPSK), Quadrature Phase Shift Keying (QPSK), 8 Quadrature AmplitudeModulation (QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and1024 QAM.
 20. The communication receiver of claim 11, wherein thecommunication receiver comprises at least one of a multi-channel headendphysical layer burst receiver, a single chip wireless modem, a singlechip DOCSIS/EuroDOCSIS cable modem, a base station receiver, a mobilereceiver, a satellite earth station, a tower receiver, a high definitiontelevision set top box receiver, and a transceiver.
 21. A communicationreceiver that is operable to perform interference cancellation, thecommunication receiver comprising: a channel equalizer that receives asignal, from a communication channel, that comprises a portion ofadditive white noise; and a canceler, communicatively coupled to thechannel equalizer, that provides an inverse, zero forcing response tothe received signal for substantial compensation of communicationchannel induced effects on the signal thereby generating a narrow peakat a frequency location of a null in a response of the communicationchannel; and wherein the narrow peak causes the white noise to becolored and to include a white noise peak thereby generating narrowbandcolored noise; and the canceler is operable to perform interferencecancellation on the narrowband colored noise.
 22. The communicationreceiver of the claim 21, wherein the canceler further comprises: avector de-spreader that de-spreads a first plurality of codes and asecond plurality of codes from a colored signal; a weight computationfunctional block that calculates a plurality of complex-valued combiningweights using the signal and the narrowband colored noise that is addedto the signal; and a linear combiner that scales the de-spread firstplurality of codes using the plurality of complex-valued combiningweights and selectively sums the de-spread first plurality of codes andone code selected from the de-spread second plurality of codes toperform interference cancellation on at least one code de-spread fromthe spread signal.
 23. The communication receiver of claim 22, whereinthe first plurality of codes comprises a plurality of unused codes; andthe second plurality of codes comprises a plurality of used codes. 24.The communication receiver of claim 23, wherein the first plurality ofcodes and the second plurality of codes comprise a total number of 128codes; the first plurality of codes comprises at least 8 codes and nomore than 32 codes; the second plurality of codes comprises a remainingplurality of codes within the total number of 128 codes not includedwithin the first plurality of codes; and the communication systemcomprises a DOCSIS 2.0 S-CDMA operable communication system.
 25. Thecommunication receiver of claim 22, wherein the weight computationfunctional block calculates the plurality of complex-valued combiningweights using both the de-spread first plurality of codes and thede-spread second plurality of codes.
 26. The communication receiver ofclaim 22, wherein the weight computation functional block calculates theplurality of complex-valued combining weights using de-spread codes thatare adjacent to the one code selected from the de-spread secondplurality of codes.
 27. The communication receiver of claim 26, whereinthe adjacent codes comprise two codes immediately adjacent to the onecode selected from the de-spread second plurality of codes; and theweight computation functional block calculates the plurality ofcomplex-valued combining weights using de-spread codes from at least oneof the first plurality of codes and the second plurality of codes thatbears preamble symbols.
 28. The communication receiver of claim 22,wherein the weight computation functional block employs at least one ofleast means square processing and least square processing to calculatethe plurality of complex-valued combining weights.
 29. The communicationreceiver of claim 21, wherein the communication receiver is operable todemodulate the signal using at least one of Binary Phase Shift Keying(BPSK), Quadrature Phase Shift Keying (QPSK), 8 Quadrature AmplitudeModulation (QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and1024 QAM.
 30. The communication receiver of claim 21, wherein thecommunication receiver comprises at least one of a multi-channel headendphysical layer burst receiver, a single chip wireless modem, a singlechip DOCSIS/EuroDOCSIS cable modem, a base station receiver, a mobilereceiver, a satellite earth station, a tower receiver, a high definitiontelevision set top box receiver, and a transceiver.
 31. A communicationreceiver that is operable to perform interference cancellation,comprising: a vector de-spreader that de-spreads a first plurality ofcodes and a second plurality of codes from a spread signal; a linearcombiner that comprises a plurality of feed-forward equalizers; andwherein each feed-forward equalizer being communicatively coupled tooutputs from each of the first plurality of codes; each feed-forwardequalizer comprises a tapped delay line and a plurality of combiningweights; each feed-forward equalizer sums its corresponding output codewith delayed and scaled versions of its corresponding output code, thedelaying and scaling being performed using the tapped delay line and theplurality of combining weights for each feed-forward equalizer; theplurality of feed-forward equalizers cooperatively provide a pluralityof feed-forward equalizer outputs; and a linear combiner that combinesthe plurality of feed-forward equalizer outputs with at least one code,selected from the second plurality of codes, to perform interferencecancellation on at least one code de-spread from the spread signal. 32.The communication receiver of claim 31, wherein each feed-forwardequalizer comprises a plurality of equalizer taps; and each equalizertap comprising a frequency selective response.
 33. The communicationreceiver of claim 31, wherein the first plurality of codes comprises aplurality of unused codes; and the second plurality of codes comprises aplurality of used codes.
 34. The communication receiver of claim 31,wherein the communication receiver is operable to demodulate the signalusing at least one of Binary Phase Shift Keying (BPSK), Quadrature PhaseShift Keying (QPSK), 8 Quadrature Amplitude Modulation (QAM), 16 QAM, 32QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and 1024 QAM.
 35. Thecommunication receiver of claim 31, wherein the communication receivercomprises at least one of a multi-channel headend physical layer burstreceiver, a single chip wireless modem, a single chip DOCSIS/EuroDOCSIScable modem, a base station receiver, a mobile receiver, a satelliteearth station, a tower receiver, a high definition television set topbox receiver, and a transceiver.
 36. A communication receiver that isoperable to perform interference cancellation, comprising: a vectorde-spreader that de-spreads a first plurality of codes and a secondplurality of codes from a spread signal; a weight computation functionalblock that calculates a plurality of complex-valued combining weightsusing the spread signal and interference contained within the spreadsignal; a linear combiner that scales the de-spread first plurality ofcodes using the plurality of complex-valued combining weights andselectively sums the scaled, de-spread first plurality of codes and onecode selected from the de-spread second plurality of codes to performinterference cancellation on at least one code de-spread from the spreadsignal; and an iterative adaptive weight functional block that isoperable to perform error calculation of a hard decision correspondingto the at least one code de-spread from the spread signal; and whereinthe iterative adaptive weight functional block updates the plurality ofcomplex-valued combining weights using the calculated error.
 37. Thecommunication receiver of claim 36, wherein the iterative adaptiveweight functional block performs least means square error processing tocalculate the error that is used to update the plurality ofcomplex-valued combining weights.
 38. The communication receiver ofclaim 36, wherein the first plurality of codes comprises a plurality ofunused codes; and the second plurality of codes comprises a plurality ofused codes.
 39. The communication receiver of claim 36, wherein thecommunication receiver is operable to demodulate the signal using atleast one of Binary Phase Shift Keying (BPSK), Quadrature Phase ShiftKeying (QPSK), 8 Quadrature Amplitude Modulation (QAM), 16 QAM, 32 QAM,64 QAM, 128 QAM, 256 QAM, 516 QAM, and 1024 QAM.
 40. The communicationreceiver of claim 36, wherein the communication receiver comprises atleast one of a multi-channel headend physical layer burst receiver, asingle chip wireless modem, a single chip DOCSIS/EuroDOCSIS cable modem,a base station receiver, a mobile receiver, a satellite earth station, atower receiver, a high definition television set top box receiver, and atransceiver.
 41. An interference cancellation method, comprising:receiving a spread signal that comprises interference; de-spreading thereceived signal using a first plurality of codes and a second pluralityof codes; calculating a plurality of complex-valued combining weightsusing the spread signal and the interference contained within the spreadsignal; scaling the de-spread first plurality of codes using theplurality of complex-valued combining weights; and selectively summingthe scaled, de-spread first plurality of codes and one code selectedfrom the de-spread second plurality of codes.
 42. The method of claim41, wherein the first plurality of codes comprises a plurality of unusedcodes; and the second plurality of codes comprises a plurality of usedcodes.
 43. The method of claim 42, wherein the first plurality of codesand the second plurality of codes comprise a total number of 128 codes;the first plurality of codes comprises at least 8 codes and no more than32 codes; the second plurality of codes comprises a remaining pluralityof codes within the total number of 128 codes not included within thefirst plurality of codes; and the communication system comprises aDOCSIS 2.0 S-CDMA operable communication system.
 44. The method of claim41, further comprising calculating the plurality of complex-valuedcombining weights using both the de-spread first plurality of codes andthe de-spread second plurality of codes.
 45. The method of claim 41,further comprising calculating the plurality of complex-valued combiningweights using de-spread codes that are adjacent to the one code selectedfrom the de-spread second plurality of codes.
 46. The method of claim45, wherein the adjacent codes comprise two codes immediately adjacentto the one code selected from the de-spread second plurality of codes.47. The method of claim 41, further comprising calculating the pluralityof complex-valued combining weights using a de-spread code from at leastone of the first plurality of codes and the second plurality of codesthat bears preamble symbols.
 48. The method of claim 41, furthercomprising employing at least one of least means square processing andleast square processing to calculate the plurality of complex-valuedcombining weights.
 49. The method of claim 41, further comprisingdemodulating the spread signal using at least one of Binary Phase ShiftKeying (BPSK), Quadrature Phase Shift Keying (QPSK), 8 QuadratureAmplitude Modulation (QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM,516 QAM, and 1024 QAM.
 50. The method of claim 41, wherein the method isperformed in at least one of a multi-channel headend physical layerburst receiver, a single chip wireless modem, a single chipDOCSIS/EuroDOCSIS cable modem, a base station receiver, a mobilereceiver, a satellite earth station, a tower receiver, a high definitiontelevision set top box receiver, and a transceiver.
 51. A synchronouscode division multiple access interference (S-CDMA) interferencecancellation method, comprising: selecting a plurality of used codesfrom a plurality of available codes; selecting a plurality of unusedcodes from the plurality of available codes; spreading a signal usingthe plurality of used codes; transmitting a spread signal; receiving thespread signal, the received spread signal comprising interference; andemploying a used projection of the received spread signal onto theplurality of used codes and an unused projection of the received spreadsignal onto the plurality of unused codes to perform interferencecancellation on the received spread signal.
 52. The method of claim 51,further comprising: computing the used projection of the received spreadsignal onto the plurality of used codes; and computing the unusedprojection of the received spread signal onto the plurality of unusedcodes.
 53. The method of claim 51, further comprising de-spreading thereceived spread signal using the plurality of used codes and theplurality of unused codes to generate the de-spread signal.
 54. Themethod of claim 51, wherein the plurality of available codes comprisesat least one of a plurality of DOCSIS 2.0 S-CDMA orthogonal codes andWalsh-Hadamard codes.
 55. The method of claim 51, wherein the pluralityof unused codes comprises at least one of a plurality of adjacent codesand a plurality of maximally spaced apart codes within the plurality ofavailable codes.
 56. The method of claim 51, wherein the plurality ofunused codes are selected employing an optimality criterion thatcomprises at least one of: selecting unused codes that have maximalcorrelation with the interference; minimizing enhancement of white noiseresulting from the interference cancellation; and minimizing residualinterference power within the received spread signal after performinginterference cancellation.
 57. The method of claim 51, wherein themethod is performed in at least one of a multi-channel headend physicallayer burst receiver, a single chip wireless modem, a single chipDOCSIS/EuroDOCSIS cable modem, a base station receiver, a mobilereceiver, a satellite earth station, a tower receiver, a high definitiontelevision set top box receiver, and a transceiver.
 58. An interferencecancellation method, comprising: selecting a plurality of used basiswaveforms from a plurality of substantially orthogonal waveforms;selecting a plurality of unused basis waveforms from the plurality ofsubstantially orthogonal waveforms; transmitting a signal using theplurality of used basis waveforms; receiving the signal, the receivedsignal comprising interference; and employing a used projection of thereceived signal onto the plurality of used basis waveforms and an unusedprojection of the received signal onto the plurality of unused basiswaveforms to perform interference cancellation on the received signal.59. The method of claim 58, further comprising: computing the usedprojection of the received signal onto the plurality of used basiswaveforms; and computing the unused projection of the received signalonto the plurality of unused basis waveforms.
 60. The method of claim58, further comprising transmitting at least one of a zero valued symboland a training symbol using the plurality of unused basis waveforms. 61.The method of claim 58, wherein a number of the plurality of unusedbasis waveforms is less than a number of the plurality of used basiswaveforms.
 62. The method of claim 58, further comprising: computing aninterference projection of the interference onto the plurality of unusedbasis waveforms; and subtracting the interference projection from theused projection.
 63. The method of claim 58, wherein the method isperformed in at least one of a multi-channel headend physical layerburst receiver, a single chip wireless modem, a single chipDOCSIS/EuroDOCSIS cable modem, a base station receiver, a mobilereceiver, a satellite earth station, a tower receiver, a high definitiontelevision set top box receiver, and a transceiver.